Magnetic tape and magnetic tape device

ABSTRACT

The magnetic tape includes a non-magnetic support; and a magnetic layer including ferromagnetic powder and a binder on the non-magnetic support, in which the total thickness of the magnetic tape is equal to or smaller than 5.30 μm, the magnetic layer includes a timing-based servo pattern, a center line average surface roughness Ra measured regarding a surface of the magnetic layer is equal to or smaller than 1.8 nm, the ferromagnetic powder is ferromagnetic hexagonal ferrite powder, the magnetic layer includes an abrasive, and a tilt cos θ of the ferromagnetic hexagonal ferrite powder with respect to a surface of the magnetic layer acquired by cross section observation performed by using a scanning transmission electron microscope is 0.85 to 1.00.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2016-124529 filed on Jun. 23, 2016. The aboveapplication is hereby expressly incorporated by reference, in itsentirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape and a magnetic tapedevice.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes (hereinafter, also simplyreferred to as “tapes”) are mainly used for data storage such as databack-up or archive. The recording of information into magnetic tape isnormally performed by recording a magnetic signal on a data band of themagnetic tape. Accordingly, data tracks are formed in the data band.

An increase in recording capacity (high capacity) of the magnetic tapeis required in accordance with a great increase in information contentin recent years. As means for realizing high capacity, a technology ofdisposing the larger amount of data tracks in a width direction of themagnetic tape by narrowing the width of the data track to increaserecording density is used.

However, when the width of the data track is narrowed and the recordingand/or reproduction of magnetic signals is performed by allowing therunning of the magnetic tape in a magnetic tape device (normallyreferred to as a “drive”), it is difficult that a magnetic headcorrectly follows the data tracks in accordance with the position changeof the magnetic tape in the width direction, and errors may easily occurat the time of recording and/or reproduction. Thus, as means forpreventing occurrence of such errors, a system using a head trackingservo using a servo signal (hereinafter, referred to as a “servosystem”) has been recently proposed and practically used (for example,see U.S. Pat. No. 5,689,384A).

SUMMARY OF THE INVENTION

In a magnetic servo type servo system among the servo systems, a servosignal (servo pattern) is formed in a magnetic layer of a magnetic tape,and this servo pattern is magnetically read to perform head tracking.More specific description is as follows.

First, a servo head reads a servo pattern formed in a magnetic layer(that is, reproduces a servo signal). A position of a magnetic head ofthe magnetic tape in a width direction is controlled in accordance withvalues (will be described later specifically) obtained by reading theservo pattern. Accordingly, when running the magnetic tape in themagnetic tape device for recording and/or reproducing a magnetic signal(information), it is possible to increase an accuracy of the position ofthe magnetic head following the data track, even when the position ofthe magnetic tape is changed in the width direction with respect to themagnetic head. By doing so, it is possible to correctly recordinformation on the magnetic tape and/or correctly reproduce informationrecorded on the magnetic tape.

As the magnetic servo type servo system described above, a timing-basedservo type system is widely used in recent years. In a timing-basedservo type servo system (hereinafter, referred to as a “timing-basedservo system”), a plurality of servo patterns having two or moredifferent shapes are formed in a magnetic layer, and a position of aservo head is recognized by an interval of time when the servo head hasread the two servo patterns having different shapes and an interval oftime when the servo head has read two servo patterns having the sameshapes. The position of the magnetic head of the magnetic tape in thewidth direction is controlled based on the position of the servo headrecognized as described above.

Meanwhile, the magnetic tape is normally used to be accommodated andcirculated in a magnetic tape cartridge. In order to increase therecording capacity for 1 reel of the magnetic tape cartridge, it isdesired to increase the total length of the magnetic tape accommodatedin 1 reel of the magnetic tape cartridge. In order to increase therecording capacity, it is necessary that the total thickness of themagnetic tape is decreased (hereinafter, referred to as “thinning”).

In addition, recently, in the magnetic tape, it is necessary thatsurface smoothness of the magnetic layer is increased. This is because,when the surface smoothness of the magnetic layer is increased,electromagnetic conversion characteristics are improved.

In consideration of these circumstances, the inventors have studied theapplication of a magnetic tape having a decreased total thickness andincreased surface smoothness of the magnetic layer to a timing-basedservo system. However, in such studies, it was clear that, a phenomenonwhich was not known in the related art occurred, in which a frequency ofoccurrence of signal defects at the time of servo signal reproducing ina timing-based servo system increases, when the total thickness of themagnetic tape is decreased and the surface smoothness of the magneticlayer is increased. As an example of such signal defects, a signaldefect called thermal asperity is exemplified. Thermal asperity is afluctuation of a reproduced waveform occurring due to a fluctuation of aresistance value of a magnetoresistive (MR) element caused by a localtemperature change occurred in the MR element, in a system including aMR head mounted with a MR element. When signal defects occur at the timeof servo signal reproducing, it is difficult to perform a head trackingin the portions where the signal defects have occurred. Therefore, it isnecessary that a frequency of occurrence of signal defects at the timeof servo signal reproducing is decreased, in order to more correctlyrecord information to the magnetic tape and/or more correctly reproducethe information recorded in the magnetic tape by using the timing-basedservo system.

Therefore, an object of the invention is to decrease a frequency ofoccurrence of signal defects in a timing-based servo system, in amagnetic tape having the decreased total thickness and the increasedsurface smoothness of the magnetic layer.

According to one aspect of the invention, there is provided a magnetictape comprising: a non-magnetic support; and a magnetic layer includingferromagnetic powder and a binder on the non-magnetic support, in whichthe total thickness of the magnetic tape is equal to or smaller than5.30 μm, the magnetic layer includes a timing-based servo pattern, acenter line average surface roughness Ra (hereinafter, also referred toas a “magnetic layer surface Ra”) measured regarding a surface of themagnetic layer is equal to or smaller than 1.8 nm, the ferromagneticpowder is ferromagnetic hexagonal ferrite powder, the magnetic layerincludes an abrasive, and a tilt cos θ (hereinafter, also simplyreferred to as “cos θ”) of the ferromagnetic hexagonal ferrite powderwith respect to a surface of the magnetic layer acquired by crosssection observation performed by using a scanning transmission electronmicroscope is 0.85 to 1.00.

In addition, in the invention and the specification, the ferromagnetichexagonal ferrite powder means an aggregate of a plurality offerromagnetic hexagonal ferrite particles. Hereinafter, particles(ferromagnetic hexagonal ferrite particles) configuring theferromagnetic hexagonal ferrite powder are also referred to as“hexagonal ferrite particles” or simply “particles”. The aggregate notonly includes an aspect in which particles configuring the aggregatedirectly come into contact with each other, but also includes an aspectin which a binder, an additive, or the like is interposed between theparticles. The points described above are also applied to various powdersuch as non-magnetic powder of the invention and the specification, inthe same manner. A calculation method of cos θ will be described laterin detail.

The “timing-based servo pattern” of the invention and the specificationis a servo pattern with which the head tracking of the timing-basedservo system can be performed.

The timing-based servo system is as described above. The servo patternwith which the head tracking of the timing-based servo system can beperformed, is formed in the magnetic layer by a servo pattern recordinghead (also referred to as a “servo write head”) as a plurality of servopatterns having two or more different shapes. As an example, theplurality of servo patterns having two or more different shapes arecontinuously disposed at regular intervals for each of the plurality ofservo patterns having the same shapes. As another example, differenttypes of the servo patterns are alternately disposed. The same shapes ofthe servo patterns do not only mean the completely same shape, and ashape error occurring due to a device such as a servo write head or thelike is allowed. The shapes of the servo pattern with which the headtracking of the timing-based servo system can be performed and thedisposition thereof in the magnetic layer are well known and specificaspect thereof will be described later. Hereinafter, the timing-basedservo pattern is also simply referred to as a servo pattern. In thespecification, as heads, a “servo write head”, a “servo head”, and a“magnetic head” are disclosed. The servo write head is a head whichperforms recording of a servo signal as described above (that is,formation of a servo pattern). The servo head is a head which performsreproduction of the servo signal (that is, reading of the servopattern), and the magnetic head is a head which performs recordingand/or reproduction of information.

In the invention and the specification, the center line average surfaceroughness Ra measured regarding the surface of the magnetic layer of themagnetic tape is a value measured with an atomic force microscope (AFM)in a region having an area of 40 μm×40 μm. As an example of themeasurement conditions, the following measurement conditions can beused. The center line average surface roughness Ra shown in exampleswhich will be described later is a value obtained by the measurementunder the following measurement conditions. In the invention and thespecification, the surface of the magnetic layer of the magnetic tape isidentical to the surface of the magnetic tape on the magnetic layerside.

The measurement is performed regarding the region having an area of 40μm×40 μm of the surface of the magnetic layer of the magnetic tape withan AFM (Nanoscope 4 manufactured by Veeco Instruments, Inc.). A scanspeed (probe movement speed) is set as 40 μm/sec and a resolution is setas 512 pixel×512 pixel.

In one aspect, the cos θ is 0.89 to 1.00.

In one aspect, the magnetic layer further includes a polyesterchain-containing compound having a weight-average molecular weight of1,000 to 80,000.

In one aspect, an activation volume of the ferromagnetic hexagonalferrite powder is 800 nm³ to 2,500 nm³.

In one aspect, the magnetic layer surface Ra is 1.2 nm to 1.8 nm.

In one aspect, the total thickness of the magnetic tape is 3.00 μm to5.30 μm.

In one aspect, the magnetic tape further comprises a non-magnetic layerincluding non-magnetic powder and a binder between the non-magneticsupport and the magnetic layer.

In one aspect, the magnetic tape includes a back coating layer includingnon-magnetic powder and a binder on a side of the non-magnetic supportopposite to a side where the magnetic layer is provided.

In one aspect, the abrasive includes alumina powder.

According to another aspect of the invention, there is provided amagnetic tape device comprising: the magnetic tape; a magnetic head; anda servo head.

According to one aspect of the invention, it is possible to provide athinned magnetic tape which includes a timing-based servo pattern in amagnetic layer having high surface smoothness and in which a frequencyof occurrence of signal defects at the time of servo signal reproducingof a timing-based servo system is decreased, and a magnetic tape devicewhich records and/or reproduces a magnetic signal to the magnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of disposition of data bands and servo bands.

FIG. 2 shows a servo pattern disposition example of a linear-tape-open(LTO) Ultrium format tape.

FIG. 3 is an explanatory diagram of an angle θ regarding a cos θ.

FIG. 4 is an explanatory diagram of another angle θ regarding a cos θ.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Magnetic Tape

According to one aspect of the invention, there is provided a magnetictape including: a non-magnetic support; and a magnetic layer includingferromagnetic powder and a binder on the non-magnetic support, in whichthe total thickness of the magnetic tape is equal to or smaller than5.30 μm, the magnetic layer includes a timing-based servo pattern, acenter line average surface roughness Ra (magnetic layer surface Ra)measured regarding a surface of the magnetic layer is equal to orsmaller than 1.8 nm, the ferromagnetic powder is ferromagnetic hexagonalferrite powder, the magnetic layer includes an abrasive, and a tilt cos9 of the ferromagnetic hexagonal ferrite powder with respect to asurface of the magnetic layer acquired by cross section observationperformed by using a scanning transmission electron microscope is 0.85to 1.00.

Hereinafter, the magnetic tape described above will be described morespecifically. The following description contains surmise of theinventors. The invention is not limited by such surmise. In addition,hereinafter, the examples are described with reference to the drawings.However, the invention is not limited to such exemplified aspects.

Magnetic Layer Surface Ra

The center line average surface roughness Ra (magnetic layer surface Ra)measured regarding the surface of the magnetic layer of the magnetictape is equal to or smaller than 1.8 nm. In the magnetic tape having themagnetic layer surface Ra equal to or smaller than 1.8 nm and the totalthickness equal to or smaller than 5.30 μm, a frequency of occurrence ofsignal defects at the time of servo signal reproducing increases in thetiming-based servo system, when no measures are provided. With respectto this, in the magnetic tape including ferromagnetic hexagonal ferritepowder and an abrasive in the magnetic layer and having the cos θ of0.85 to 1.00, it is possible to prevent the occurrence of signal defectsat the time of servo signal reproducing, although the magnetic layersurface Ra is equal to or smaller than 1.8 nm and the total thickness isequal to or smaller than 5.30 μm. The surmise of the inventors regardingthis point will be described later. In addition, the magnetic tapehaving the magnetic layer surface Ra equal to or smaller than 1.8 nm canshow excellent electromagnetic conversion characteristics. From aviewpoint of further improvement of the electromagnetic conversioncharacteristics, the magnetic layer surface Ra is preferably equal to orsmaller than 1.7 nm and more preferably equal to or smaller than 1.6 nm.In addition, the magnetic layer surface Ra can be, for example, equal toor greater than 1.2 nm or equal to or greater than 1.3 nm. Here, a lowmagnetic layer surface Ra is preferable from a viewpoint of theimprovement of the electromagnetic conversion characteristics, and thus,the magnetic layer surface Ra may be smaller than the exemplifiedvalues.

The magnetic layer surface Ra can be controlled by a well-known method.For example, the magnetic layer surface Ra can be changed in accordancewith a size of various powder (for example, ferromagnetic powder,non-magnetic powder which may be arbitrarily included, and the like)included in the magnetic layer or manufacturing conditions of themagnetic tape, and thus, by adjusting these, it is possible to obtain amagnetic tape having the magnetic layer surface Ra equal to or smallerthan 1.8 nm.

Timing-Based Servo Pattern

The magnetic tape includes a timing-based servo pattern in the magneticlayer. The timing-based servo pattern is the servo pattern describedabove. In a magnetic tape used in a linear recording system which iswidely used as a recording system of the magnetic tape device, forexample, a plurality of regions (referred to as “servo bands”) whereservo patterns are formed are normally present in the magnetic layeralong a longitudinal direction of the magnetic tape. A region interposedbetween two servo bands is referred to as a data band. The recording ofmagnetic signals (information) is performed on the data band and aplurality of data tracks are formed in each data band along thelongitudinal direction.

FIG. 1 shows an example of disposition of data bands and servo bands. InFIG. 1, a plurality of servo bands 10 are disposed to be interposedbetween guide bands 12 in a magnetic layer of a magnetic tape 1. Aplurality of regions 11 each of which is interposed between two servobands are data bands. The servo pattern is a magnetized region and isformed by magnetizing a specific region of the magnetic layer by a servowrite head. The region magnetized by the servo write head (positionwhere a servo pattern is formed) is determined by standards. Forexample, in a LTO Ultrium format tape which is based on a localstandard, a plurality of servo patterns tilted in a tape width directionas shown in FIG. 2 are formed on a servo band when manufacturing amagnetic tape. Specifically, in FIG. 2, a servo frame SF on the servoband 10 is configured with a servo sub-frame 1 (SSF1) and a servosub-frame 2 (SSF2). The servo sub-frame 1 is configured with an A burst(in FIG. 2, reference numeral A) and a B burst (in FIG. 2, referencenumeral B). The A burst is configured with servo patterns A1 to A5 andthe B burst is configured with servo patterns B1 to B5. Meanwhile, theservo sub-frame 2 is configured with a C burst (in FIG. 2, referencenumeral C) and a D burst (in FIG. 2, reference numeral D). The C burstis configured with servo patterns C1 to C4 and the D burst is configuredwith servo patterns D1 to D4. Such 18 servo patterns are disposed in thesub-frames in the arrangement of 5, 5, 4, 4, as the sets of 5 servopatterns and 4 servo patterns, and are used for recognizing the servoframes. FIG. 2 shows one servo frame for description. However, inpractice, in a magnetic layer of the magnetic tape in which a headtracking is performed in a timing-based servo system, a plurality ofservo frames are disposed in each servo band in a running direction. InFIG. 2, an arrow shows the running direction. The servo headsequentially reads the servo patterns in the plurality of servo frames,while running on the magnetic layer.

In the timing-based servo system, a position of a servo head isrecognized based on an interval of time when the servo head has read thetwo servo patterns (reproduced servo signals) having different shapesand an interval of time when the servo head has read two servo patternshaving the same shapes. The time interval is normally obtained as a timeinterval of a peak of a reproduced waveform of a servo signal. Forexample, in the aspect shown in FIG. 2, the servo pattern of the A burstand the servo pattern of the C burst are servo patterns having the sameshapes, and the servo pattern of the B burst and the servo pattern ofthe D burst are servo patterns having the same shapes. The servo patternof the A burst and the servo pattern of the C burst are servo patternshaving the shapes different from the shapes of the servo pattern of theB burst and the servo pattern of the D burst. An interval of the timewhen the two servo patterns having different shapes are read by theservo head is, for example, an interval between the time when any servopattern of the A burst is read and the time when any servo pattern ofthe B burst is read. An interval of the time when the two servo patternshaving the same shapes are read by the servo head is, for example, aninterval between the time when any servo pattern of the A burst is readand the time when any servo pattern of the C burst is read. Thetiming-based servo system is a system supposing that occurrence of adeviation of the time interval is due to a position change of themagnetic tape in the width direction, in a case where the time intervalis deviated from the set value. The set value is a time interval in acase where the magnetic tape runs without occurring the position changein the width direction. In the timing-based servo system, the magnetichead is moved in the width direction in accordance with a degree of thedeviation of the obtained time interval from the set value.Specifically, as the time interval is greatly deviated from the setvalue, the magnetic head is greatly moved in the width direction. Thispoint is applied to not only the aspect shown in FIG. 1 and FIG. 2, butalso to entire timing-based servo systems. When signal defects occur atthe time of servo signal reproducing in a magnetic tape device using thetiming-based servo system described above, it is difficult to obtainmeasurement results of the time intervals in portions (servo frames)where the defects have occurred. As a result, it is partially difficultto perform positioning of the head by moving the magnetic head in awidth direction, when recording or reproducing magnetic signals(information) by the magnetic head by running the magnetic tape. Inregards to this point, in the studies of the inventors, it was foundthat the signal defects significantly occur at the time of servo signalreproducing, in the magnetic tape having the total thickness equal to orsmaller than 5.30 μm and the magnetic layer surface Ra equal to orsmaller than 1.8 nm. The inventors have thought that a reason of theoccurrence of signal defects at the time of servo signal reproducing isdisturbance of smooth sliding between the servo head and the surface ofthe magnetic layer (hereinafter, referred to as “deterioration ofsliding properties”). The inventors have surmised that a reason of adecrease in sliding properties may be a contact state between the servohead and the surface of the magnetic layer which is different betweenthe magnetic tape having the total thickness equal to or smaller than5.30 μm and the magnetic layer surface Ra equal to or smaller than 1.8nm and a magnetic tape of the related art. However, this is merely asurmise.

With respect this, as a result of the intensive studies of theinventors, it was clear that the occurrence of signal defects at thetime of servo signal reproducing can be prevented by setting the cos θto be 0.85 to 1.00. The surmise of the inventors regarding this pointwill be described later.

Cos θ

In the magnetic tape, the tilt cos θ of the ferromagnetic hexagonalferrite powder with respect to the surface of the magnetic layeracquired by the cross section observation performed by using a scanningtransmission electron microscope is 0.85 to 1.00. The cos θ is morepreferably equal to or greater than 0.89, even more preferably equal toor greater than 0.90, still more preferably equal to or greater than0.92, and still even more preferably equal to or greater than 0.95.Meanwhile, in a case where all of the hexagonal ferrite particles havingan aspect ratio and a length in a long axis direction which will bedescribed later are present to be parallel to the surface of themagnetic layer, the cos θ becomes 1.00 which is the maximum value.According to the research of the inventor, it is found that, as thevalue of the cos θ increases, the frequency of occurrence of signaldefects decreases at the time of servo signal reproducing in thetiming-based servo system. That is, in the magnetic tape having thetotal thickness equal to or smaller than 5.30 μm and the magnetic layersurface Ra equal to or smaller than 1.8 nm, a great value of the cos θis preferable, from a viewpoint of further decreasing the frequency ofoccurrence of signal defects at the time of servo signal reproducing inthe timing-based servo system. Accordingly, in the magnetic tape, theupper limit of the cos θ is equal to or smaller than 1.00. The cos θ maybe, for example, equal to or smaller than 0.99. However, as describedabove, a great value of the cos θ is preferable, and thus, the cos θ mayexceed 0.99.

Calculation Method of Cos θ

The cos θ is acquired by the cross section observation performed byusing a scanning transmission electron microscope (hereinafter, alsoreferred to as a “STEM”). The cos θ of the invention and thespecification is a value measured and calculated by the followingmethod.

(1) A cross section observation sample is manufactured by performing thecutting out from an arbitrarily determined position of the magnetic tapewhich is a target for acquiring the cos θ. The manufacturing of thecross section observation sample is performed by focused ion beam (FIB)processing using a gallium ion (Ga⁺) beam. A specific example of such amanufacturing method will be described later with Examples.

(2) The manufactured cross section observation sample is observed withthe STEM, and a STEM images are captured. The STEM images are capturedat positions of the same cross section observation sample arbitrarilyselected, except for selecting so that the imaging ranges are notoverlapped, and total 10 images are obtained. The STEM image is aSTEM-high-angle annular dark field (HAADF) image which is captured at anacceleration voltage of 300 kV and an imaging magnification of 450,000,and the imaging is performed so that entire region of the magnetic layerin a thickness direction is included in one image. The entire region ofthe magnetic layer in the thickness direction is a region from thesurface of the magnetic layer observed in the cross section observationsample to an interface between the magnetic layer and the adjacent layeror the non-magnetic support. The adjacent layer is a non-magnetic layer,in a case where the magnetic tape which is a target for acquiring thecos θ includes the non-magnetic layer which will be described laterbetween the magnetic layer and the non-magnetic support. Meanwhile, in acase where the magnetic tape which is a target for acquiring the cos θincludes the magnetic layer directly on the non-magnetic support, theinterface is an interface between the magnetic layer and thenon-magnetic support.

(3) In each STEM image obtained as described above, a linear lineconnecting both ends of a line segment showing the surface of themagnetic layer is determined as a reference line. In a case where theSTEM image is captured so that the magnetic layer side of the crosssection observation sample is positioned on the upper side of the imageand the non-magnetic support side is positioned on the lower side, forexample, the linear line connecting both ends of the line segmentdescribed above is a linear line connecting an intersection between aleft side of the image (normally, having a rectangular or square shape)of the STEM image and the line segment, and an intersection between aright side of the STEM image and the line segment to each other.

(4) Among the hexagonal ferrite particles observed in the STEM image, anangle θ formed by the reference line and the long axis direction of thehexagonal ferrite particles (primary particles) having an aspect ratioin a range of 1.5 to 6.0 and a length in the long axis direction equalto or greater than 10 nm is measured, and regarding the measured angleθ, the cos θ is calculated as a cos θ based on a unit circle. Thecalculation of the cos θ is performed with 30 particles arbitrarilyextracted from the hexagonal ferrite particles having the aspect ratioand the length in the long axis direction in each STEM image.

(5) The measurement and the calculation are respectively performed for10 images, the values of the acquired cos θ of the 30 hexagonal ferriteparticles of each image, that is, 300 hexagonal ferrite particles intotal of the 10 images, are averaged. The arithmetical mean acquired asdescribed above is set as the tilt cos θ of the ferromagnetic hexagonalferrite powder with respect to the surface of the magnetic layeracquired by the cross section observation performed by using thescanning transmission electron microscope.

Here, the “aspect ratio” observed in the STEM image is a ratio of“length in the long axis direction/length in a short axis direction” ofthe hexagonal ferrite particles.

The “long axis direction” means a direction when an end portion close tothe reference line and an end portion far from the reference line areconnected to each other, among the end portions which are most separatedfrom each other, in the image of one hexagonal ferrite particle observedin the STEM image. In a case where a line segment connecting one endportion and the other end portion is parallel with the reference line, adirection parallel to the reference line becomes the long axisdirection.

The “length in the long axis direction” means a length of a line segmentdrawn by connecting end portions which are most separated from eachother, in the image of one hexagonal ferrite particle observed in theSTEM image. Meanwhile, the “length in the short axis direction” means alength of the longest line segment, among the line segments connectingtwo intersections between an outer periphery of the image of theparticle and a perpendicular line with respect to the long axisdirection.

In addition, the angle θ formed by the reference line and the tilt ofthe particle in the long axis direction is determined to be in a rangeof 0° to 90°, by setting an angle of the long axis direction parallel tothe reference line as 0°. Hereinafter, the angle θ will be furtherdescribed with reference to the drawings.

FIG. 3 and FIG. 4 are explanatory diagrams of the angle θ. In FIG. 3 andFIG. 4, a reference numeral 101 indicates a line segment (length in thelong axis direction) drawn by connecting end portions which are mostseparated from each other, a reference numeral 102 indicates thereference line, and a reference numeral 103 indicates an extended lineof the line segment (reference numeral 101). In this case, as the angleformed by the reference line 102 and the extended line 103, θ1 and θ2are exemplified as shown in FIG. 3 and FIG. 4. Here, a smaller angle isused from the θ1 and θ2, and this is set as the angle θ. Accordingly, inthe aspect shown in FIG. 3, the θ1 is set as the angle θ, and in theaspect shown in FIG. 4, θ2 is set as the angle θ. A case where θ1=θ2 isa case where the angle θ=90°. The cos θ based on the unit circle becomes1.00, in a case where the θ=0°, and becomes 0, in a case where theθ=90°.

The magnetic tape includes the abrasive and the ferromagnetic hexagonalferrite powder in the magnetic layer, and cos θ is 0.85 to 1.00. Theinventors have thought that hexagonal ferrite particles satisfying theaspect ratio and the length in the long axis direction among thehexagonal ferrite particles configuring the ferromagnetic hexagonalferrite powder included in the magnetic layer can support the abrasive.The inventors have thought that this point contributes the prevention ofthe occurrence of signal defects at the time of servo signal reproducingof the timing-based servo system in the magnetic tape. This point willbe further described below.

The abrasive can impart a function (hereinafter, referred to as“abrasion resistance”) of removing foreign materials (hereinafter,referred to as “attached materials”) attached to the servo head, to thesurface of the magnetic layer. When the surface of the magnetic layerexhibits abrasion resistance, it is possible to remove the attachedmaterial generated and attached to the servo head due to the chipping ofa part of the surface of the magnetic layer caused by the running of theservo head on the magnetic layer. However, the inventors have surmisedthat, when the surface of the magnetic layer does not sufficientlyexhibit the abrasion resistance, the servo head runs on the magneticlayer in a state where the attached material is attached to the servohead, and thus, the signal defects occur due to the effect of theattached material. The inventors have thought that a decrease inabrasion resistance of the surface of the magnetic layer occurs due topressing of the abrasive present in the vicinity of the surface of themagnetic layer into the magnetic layer due to the contact with the servohead.

With respect to this, it is considered that the pressing of the abrasivepresent in the vicinity of the surface of the magnetic layer into themagnetic layer due to the contact with the servo head can be preventedby supporting the abrasive by the hexagonal ferrite particles satisfyingthe aspect ratio and the length in the long axis direction. Thus, theinventors have surmised that it is possible to prevent a decrease inabrasion resistance of the surface of the magnetic layer, and as aresult, the occurrence of signal defects due to the effect of theattached material attached to the servo head can be prevented at thetime of servo signal reproducing. However, this is merely a surmise.

A squareness ratio is known as an index of a presence state (orientationstate) of the ferromagnetic hexagonal ferrite powder of the magneticlayer. However, according to the studies of the inventors, an excellentcorrelation was not observed between the squareness ratio and thefrequency of occurrence of signal defects at the time of servo signalreproducing. The squareness ratio is a value indicating a ratio ofresidual magnetization with respect to saturated magnetization, and ismeasured using all of the particles as targets, regardless of the shapesand size of the particles included in the ferromagnetic hexagonalferrite powder. With respect to this, the cos θ is a value measured byselecting the hexagonal ferrite particles having the aspect ratio andthe length in the long axis direction in the ranges described above. Theinventors have thought that an excellent correlation may be observedbetween the cos θ and the frequency of occurrence of signal defects atthe time of servo signal reproducing, depending on the cos θ. However,this is merely a surmise, and the invention is not limited thereto.

Adjustment Method of Cos θ

The magnetic tape can be manufactured through a step of applying amagnetic layer forming composition onto the non-magnetic support. As anadjustment method of the cos θ, a method of controlling a dispersionstate of the ferromagnetic hexagonal ferrite powder of the magneticlayer forming composition is used. Regarding this viewpoint, theinventors have thought that, as dispersibility of the ferromagnetichexagonal ferrite powder in the magnetic layer forming composition(hereinafter, also simply referred to as “dispersibility of theferromagnetic hexagonal ferrite powder” or “dispersibility”) isincreased, the hexagonal ferrite particles having the aspect ratio andthe length in the long axis direction in the ranges described above inthe magnetic layer formed by using this magnetic layer formingcomposition are easily oriented in a state closer to parallel to thesurface of the magnetic layer. As means for increasing dispersibility,any one or both of the following methods (1) and (2) are used.

(1) Adjustment of Dispersion Conditions

(2) Use of Dispersing Agent

In addition, as means for increasing dispersibility, a method ofseparately dispersing the ferromagnetic hexagonal ferrite powder and theabrasive is also used. The separate dispersing is more specifically amethod of preparing the magnetic layer forming composition through astep of mixing a magnetic solution including the ferromagnetic hexagonalferrite powder, a binder, and a solvent (here, substantially notincluding an abrasive), and an abrasive liquid including an abrasive anda solvent with each other. By performing the mixing after separatelydispersing the abrasive and the ferromagnetic hexagonal ferrite powderas described above, it is possible to increase the dispersibility of theferromagnetic hexagonal ferrite powder of the magnetic layer formingcomposition. The expression of “substantially not including an abrasive”means that the abrasive is not added as a constituent component of themagnetic solution, and a small amount of the abrasive present asimpurities by being mixed without intention is allowed. In addition, itis also preferable that any one or both of the methods (1) and (2) arecombined with the separate dispersion described above. In this case, bycontrolling the dispersion state of the ferromagnetic hexagonal ferritepowder of the magnetic solution, it is possible to control thedispersion state of the ferromagnetic hexagonal ferrite powder of themagnetic layer forming composition obtained through the step of mixingthe magnetic solution with the abrasive liquid.

Hereinafter, specific aspects of the methods (1) and (2) will bedescribed.

(1) Adjustment of Dispersion Conditions

A dispersing process of the magnetic layer forming composition,preferably the magnetic solution can be performed by adjusting thedispersion conditions thereof by using a well-known dispersing method.The dispersion conditions of the dispersing process, for example,include the types of a dispersion device, the types of dispersion mediaused in the dispersion device, and a retention time in the dispersiondevice (hereinafter, also referred to as a “dispersion retention time”).

As the dispersion device, various well-known dispersion devices using ashear force such as a ball mill, a sand mill, or a homomixer. Adispersing process having two or more stages may be performed byconnecting two or more dispersion devices to each other, or differentdispersion devices may be used in combination. A circumferential speedof a tip of the dispersion device is preferably 5 to 20 m/sec and morepreferably 7 to 15 m/sec.

As the dispersion medium, ceramic beads or glass beads are used, andzirconia beads are preferable. Two or more types of beads may be used incombination. A particle diameter of the dispersion medium is, forexample, 0.03 to 1 mm and is preferably 0.05 to 0.5 mm. In a case ofperforming the dispersing process having two or more stages byconnecting the dispersion devices as described above, the dispersionmedium having different particle diameters may be used in each stage. Itis preferable that the dispersion medium having a smaller particlediameter is used, as the stages are passed. A filling percentage of thedispersion medium can be, for example, 30% to 80% and preferably 50% to80% based on the volume.

The dispersion retention time may be suitably set b considering thecircumferential speed of the tip of the dispersion device and thefilling percentage of the dispersion medium, and can be, for example, 15to 45 hours and preferably 20 to 40 hours. In a case of performing thedispersing process having two or more stages by connecting thedispersion devices as described above, the total dispersion retentiontime of each stage is preferably in the range described above. Byperforming the dispersing process described above, it is possible toincrease the dispersibility of the ferromagnetic hexagonal ferritepowder and to adjust the cos θ to be 0.85 to 1.00.

(2) Use of Dispersing Agent

It is possible to increase the dispersibility of the ferromagnetichexagonal ferrite powder by using a dispersing agent at the time ofpreparing the magnetic layer forming composition, preferably at the timeof preparing the magnetic solution. Here, the dispersing agent is acomponent which can increase the dispersibility of the ferromagnetichexagonal ferrite powder of the magnetic layer forming compositionand/or the magnetic solution, compared to a state where the agent is notpresent. It is also possible to control the dispersion state of theferromagnetic hexagonal ferrite powder by changing the type and theamount of the dispersing agent included in the magnetic layer formingcomposition and/or the magnetic solution. As the dispersing agent, adispersing agent which prevents aggregation of the hexagonal ferriteparticles configuring the ferromagnetic hexagonal ferrite powder andimparts suitable plasticity to the magnetic layer is also preferablyused, from a viewpoint of increasing durability of the magnetic layer.

As an aspect of the dispersing agent preferable for improving thedispersibility of the ferromagnetic hexagonal ferrite powder, apolyester chain-containing compound can be used. The polyesterchain-containing compound is preferable from a viewpoint of impartingsuitable plasticity to the magnetic layer. Here, the polyester chain isshown as E in General Formula A which will be described later. Specificaspects thereof include a polyester chain contained in General Formula1, a polyester chain represented by Formula 2-A, and a polyester chainrepresented by Formula 2-B which will be described later. The inventorshave surmised that, by mixing the polyester chain-containing compoundwith the magnetic layer forming composition and/or the magnetic solutiontogether with the ferromagnetic hexagonal ferrite powder, it is possibleto prevent aggregation of particles, due to the polyester chaininterposed between the hexagonal ferrite particles. However, this ismerely the surmise, and the invention is not limited thereto. Aweight-average molecular weight of the polyester chain-containingcompound is preferably equal to or greater than 1,000, from a viewpointof improving the dispersibility of the ferromagnetic hexagonal ferritepowder. In addition, the weight-average molecular weight of thepolyester chain-containing compound is preferably equal to or smallerthan 80,000. The inventors have thought that the polyesterchain-containing compound having a weight-average molecular weight equalto or smaller than 80,000 can increase the durability of the magneticlayer by exhibiting an operation of a plasticizer. The weight-averagemolecular weight of the invention and the specification is a valueobtained by performing reference polystyrene conversion of a valuemeasured by gel permeation chromatography (GPC). Specific examples ofthe measurement conditions will be described later. In addition, thepreferred range of the weight-average molecular weight will be alsodescribed later.

As a preferred aspect of the polyester chain-containing compound, acompound having a partial structure represented by the following GeneralFormula A is used. In the invention and the specification, unlessotherwise noted, a group disclosed may include a substituent or may benon-substituted. In a case where a given group includes a substituent,examples of the substituent include an alkyl group (for example, alkylgroup having 1 to 6 carbon atoms), a hydroxyl group, an alkoxy group(for example, alkoxy group having 1 to 6 carbon atoms), a halogen atom(for example, a fluorine atom, a chlorine atom, or a bromine atom), acyano group, an amino group, a nitro group, an acyl group, carboxyl(salt) group. In addition, the “number of carbon atoms” of the groupincluding a substituent means the number of carbon atoms of a portionnot including a substituent.

In General Formula A, Q represents —O—, —CO—, —S—, —NR^(a)—, or a singlebond, T and R^(a) each independently represent a hydrogen atom or amonovalent substituent, E represents —(O-L^(A)-CO)a- or —(CO-L^(A)-O)a-,L^(A) represents a divalent linking group, a represents an integer equalto or greater than 2, b represents an integer equal to or greater than1, and * represents a bonding site with another partial structureconfiguring the polyester chain-containing compound.

In General Formula A, the number of L^(A) included is a value of a×b. Inaddition, the numbers of T and Q included are respectively the value ofb. In a case where a plurality of L^(A) are included in General FormulaA, the plurality of L^(A) may be the same as each other or differentfrom each other. The same applies to T and Q.

It is considered that the compound described above can preventaggregation of hexagonal ferrite particles due to a steric hindrancecaused by the partial structure, in the magnetic solution and themagnetic layer forming composition.

As a preferred aspect of the polyester chain-containing compound, acompound including a group which can be adsorbed to the surface of thehexagonal ferrite particles or the partial structure (hereinafter,referred to as an “adsorption part”) together with the polyester chainin a molecule is used. It is preferable that the polyester chain isincluded in the partial structure represented by General Formula A. Inaddition, it is more preferable that the partial structure and theadsorption part represented by General Formula A form a bond through *in General Formula A.

In one aspect, the adsorption part can be a functional group (polargroup) having polarity to be an adsorption point to the surface of thehexagonal ferrite particles. As a specific example, at least one polargroup selected from a carboxyl group (—COOH) and a salt thereof(—COO⁻M⁺), a sulfonic acid group (—SO₃H) and a salt thereof (—SO₃ ⁻M⁺),a sulfuric acid group (—OSO₃H) and a salt thereof (—OSO₃ ⁻M⁺), aphosphoric acid group (—P═O(OH)₂) and a salt thereof (—P═O(O⁻M⁺)₂), anamino group (—NR₂), —N⁺R₃, an epoxy group, a thiol group (—SH), and acyano group (—CN) (here, M⁺ represents a cation such as an alkali metalion and R represents a hydrogen atom or a hydrocarbon group) can beused. In addition, the “carboxyl (salt) group” means one or both of acarboxyl group and a salt thereof (carboxylic salt). The carboxylic saltis a state of a salt of the carboxyl group (—COOH) as described above.

As one aspect of the adsorption part, a polyalkyleneimine chain can alsobe used.

The types of the bond formed by the partial structure and the adsorptionpart represented by General Formula A are not particularly limited. Sucha bond is preferably selected from the group consisting of a covalentbond, a coordinate bond, and an ion bond, and bonds of different typesmay be included in the same molecule. It is considered that byefficiently performing the adsorption with respect to the hexagonalferrite particles through the adsorption part, it is possible to furtherincrease an aggregation prevention effect of the hexagonal ferriteparticles based on the steric hindrance caused by the partial structurerepresented by General Formula A.

In one aspect, the polyester chain-containing compound can include atleast one polyalkyleneimine chain. The polyester chain-containingcompound can preferably include a polyester chain in the partialstructure represented by General Formula A. As a preferred example ofthe polyester chain-containing compound, a polyalkyleneimine derivativeincluding a polyester chain selected from the group consisting of apolyester chain represented by the following Formula 2-A and a polyesterchain represented by the following Formula 2-B as General Formula A isused. These examples will be described later in detail.

L¹ in Formula 2-A and L² in Formula 2-B each independently represent adivalent linking group, b11 in Formula 2-A and b21 in Formula 2-B eachindependently represent an integer equal to or greater than 2, b12 inFormula 2-A and b22 in Formula 2-B each independently represent 0 or 1,and X¹ in Formula 2-A and X² in Formula 2-B each independently representa hydrogen atom or a monovalent substituent.

In General Formula A, Q represents —O—, —CO—, —S—, —NR^(a)—, or a singlebond, and is preferably a portion represented by X in General Formula 1which will be described later, (—CO—)b12 in Formula 2-A or (—CO—)b22 inFormula 2-B.

In General Formula A, T and R^(a) each independently represent ahydrogen atom or a monovalent substituent and is preferably a portionrepresented by R in General Formula 1 which will be described later, X¹in Formula 2-A or X² in Formula 2-B.

In General Formula A, E represents —(O-L^(A)-CO)a- or —(CO-L^(A)-O)a-,L^(A) represents a divalent linking group, and a represents an integerequal to or greater than 2.

As a divalent linking group represented by L^(A), L in General Formula 1which will be described later, L¹ in Formula 2-A or L² in Formula 2-B ispreferably used.

In one aspect, the polyester chain-containing compound can include atleast one group selected from the group consisting of a carboxyl groupand a carboxylic salt. Such a polyester chain-containing compound canpreferably include a polyester chain in the partial structurerepresented by General Formula A. As a preferred example of thepolyester chain-containing compound, a compound represented by thefollowing General Formula 1 is used.

Compound Represented by General Formula 1

General Formula 1 is as described below.

(In General Formula 1, X represents —O—, —S—, or —NR¹—, R and R¹ eachindependently represent a hydrogen atom or a monovalent substituent, Lrepresents a divalent linking group, Z represents a n-valent partialstructure including at least one group (carboxyl (salt) group) selectedfrom the group consisting of a carboxyl group and a carboxylic salt, mrepresents an integer equal to or greater than 2, and n represents aninteger equal to or greater than 1.)

In General Formula 1, the number of L included is a value of m×n. Inaddition, the numbers of R and X included are respectively the value ofn. In a case where a plurality of L are included in General Formula 1,the plurality of L may be the same as each other or different from eachother. The same applies to R and X.

The compound represented by General Formula 1 has a structure (polyesterchain) represented by —((C═O)-L-O)m-, and a carboxyl (salt) group isincluded in the Z part as the adsorption part. It is considered that,when the compound represented by General Formula 1 is effectivelyadsorbed to the hexagonal ferrite particles by setting the carboxyl(salt) group included in the Z part as the adsorption part to thesurface of the hexagonal ferrite particles, it is possible to preventaggregation of the hexagonal ferrite particles caused by sterichindrance caused by the polyester chain.

In General Formula 1, X represents —O—, —S—, or —NR¹—, and R¹ representsa hydrogen atom or a monovalent substituent. As the monovalentsubstituent represented by R¹, an alkyl group, a hydroxyl group, analkoxy group, a halogen atom, a cyano group, an amino group, a nitrogroup, an acyl group, and a carboxyl (salt) group which is thesubstituent described above can be used, an alkyl group is preferablyused, an alkyl group having 1 to 6 carbon atoms is more preferably used,and a methyl group or an ethyl group is even more preferably used. R¹ isstill more preferably a hydrogen atom. X preferably represents —O—.

R represents a hydrogen atom or a monovalent substituent. R preferablyrepresents a monovalent substituent. As the monovalent substituentrepresented by R, a monovalent group such as an alkyl group, an arylgroup, a heteroaryl group, an alicyclic group, or a nonaromaticheterocyclic group, and a structure in which a divalent linking group isbonded to the monovalent group (that is, R has a structure in which adivalent linking group is bonded to the monovalent group and is amonovalent substituent bonding with X through the divalent linkinggroup) can be used, for example. As the divalent linking group, adivalent linking group configured of a combination of one or two or moreselected from the group consisting of —C(═O)—O—, —O—, —C(═O)—NR¹⁰— (R¹⁰represents a hydrogen atom or an alkyl group having 1 to 4 carbonatoms), —O—C(═O)—NH—, a phenylene group, an alkylene group having 1 to30 carbon atoms, and an alkenylene group having 2 to 30 carbon atoms canbe used, for example. As a specific example of the monovalentsubstituent represented by R, the following structures are used, forexample. In the following structures, * represents a bonding site withX. However, R is not limited to the following specific example.

In General Formula 1, L represents a divalent linking group. As thedivalent linking group, a divalent linking group which is configured ofa combination of one or two or more selected from the group consistingof an alkylene group which may have a linear, branched, or cyclicstructure, an alkenylene group which may have a linear, branched, orcyclic structure, —C(═O)—, —O—, and an arylene group, and which mayinclude a substituent in the divalent linking group or a halogen atom asan anion can be used. More specifically, a divalent linking groupconfigured of a combination of one or two or more selected from analkylene group having 1 to 12 carbon atoms which may have a linear,branched, or cyclic structure, an alkenylene group having 1 to 6 carbonatoms which may have a linear, branched, or cyclic structure, —C(═O)—,—O—, and a phenylene group can be used. The divalent linking group ispreferably a divalent linking group formed of 1 to 10 carbon atoms, 0 to10 oxygen atoms, 0 to 10 halogen atoms, and 1 to 30 hydrogen atoms. As aspecific example, an alkylene group and the following structures areused. In the following structures, * represents a bonding site with theother structure in General Formula 1. However, the divalent linkinggroup is not limited to the following specific example.

L is preferably an alkylene group, more preferably an alkylene grouphaving 1 to 12 carbon atoms, even more preferably an alkylene grouphaving 1 to 5 carbon atoms, and still more preferably a non-substitutedalkylene group having 1 to 5 carbon atoms.

Z represents an n-valent partial structure including at least one group(carboxyl (salt) group) selected from the group consisting of a carboxylgroup and a carboxylic salt.

The number of the carboxyl (salt) group included in Z is at least 1,preferably equal to or greater than 2, and more preferably 2 to 4, forone Z.

Z can have a structure of one or more selected from the group consistingof a linear structure, a branched structure, and a cyclic structure.From a viewpoint of easiness of synthesis, Z is preferably a reactiveresidue of a carboxylic acid anhydride. For example, as a specificexample, the following structures are used. In the followingstructures, * represents a bonding site with the other structure inGeneral Formula 1. However, Z is not limited to the following specificexample.

The carboxylic acid anhydride is a compound having a partial structurerepresented by —(C═O)—O—(C═O)—. In the carboxylic acid anhydride, thepartial structure becomes a reactive site, and an oxygen atom and Z of—((C═O)-L-O)m- in General Formula 1 are bonded to each other through acarbonyl bond (—(C═O)—), and a carboxyl (salt) group is obtained. Thepartial structure generated as described above is a reactive residue ofa carboxylic acid anhydride. By synthesizing the compound represented byGeneral Formula 1 by using a compound having one partial structure—(C═O)—O—(C═O)—, as the carboxylic acid anhydride, it is possible toobtain a compound represented by General Formula 1 including amonovalent reactive residue of the carboxylic acid anhydride, and it ispossible to obtain a compound represented by General Formula 1 includinga divalent reactive residue of the carboxylic acid anhydride, by usingthe compound having two partial structures described above. The sameapplies to the compound represented by General Formula 1 including atrivalent or higher reactive residue of the carboxylic acid anhydride.As described above, n is an integer equal to or greater than 1, is, forexample, an integer of 1 to 4, and is preferably an integer of 2 to 4.

It is possible to obtain a compound represented by General Formula 1 ina case of n=2, by using the tetracarboxylic acid anhydride, for example,as the carboxylic acid anhydride. The tetracarboxylic acid anhydride isa carboxylic acid anhydride having two partial structures describedabove in one molecule, by dehydration synthesis of two carboxyl groups,in the compound including four carboxyl groups in one molecule. InGeneral Formula 1, the compound in which Z represents a reactive residueof the tetracarboxylic acid anhydride is preferable, from viewpoints offurther improving dispersibility of ferromagnetic hexagonal ferritepowder and durability of the magnetic layer. Examples of thetetracarboxylic acid anhydride include various tetracarboxylic acidanhydrides such as aliphatic tetracarboxylic acid anhydride, aromatictetracarboxylic acid anhydride, and polycyclic tetracarboxylic acidanhydride.

As the aliphatic tetracarboxylic acid anhydride, for example, variousaliphatic tetracarboxylic acid anhydrides disclosed in a paragraph 0040of JP2016-071926A can be used. As the aromatic tetracarboxylic acidanhydride, for example, various aromatic tetracarboxylic acid anhydridesdisclosed in a paragraph 0041 of JP2016-071926A can be used. As thepolycyclic tetracarboxylic acid anhydride, various polycyclictetracarboxylic acid anhydrides disclosed in a paragraph 0042 ofJP2016-071926A can be used.

In General Formula 1, m represents an integer equal to or greater than2. As described above, it is thought that the structure (polyesterchain) represented by —((C═O)-L-O)m- of the compound represented byGeneral Formula 1 contributes to the improvement of dispersibility andthe durability. From these viewpoints, m is preferably an integer of 5to 200, more preferably an integer of 5 to 100, and even more preferablyan integer of 5 to 60.

Weight-Average Molecular Weight

The weight-average molecular weight of the compound represented byGeneral Formula 1 is preferably 1,000 to 80,000 as described above andmore preferably 1,000 to 20,000. The weight-average molecular weight ofthe compound represented by General Formula 1 is even more preferablysmaller than 20,000, further more preferably equal to or smaller than12,000, and sill more preferably equal to or smaller than 10,000. Inaddition, the weight-average molecular weight of the compoundrepresented by General Formula 1 is preferably equal to or greater than1,500 and more preferably equal to or greater than 2,000. Regarding thecompound represented by General Formula 1, the weight-average molecularweight shown in Examples which will be described later is a valueobtained by performing reference polystyrene conversion of a valuemeasured by GPC under the following measurement conditions. In addition,the weight-average molecular weight of a mixture of two or more kinds ofstructural isomers is a weight-average molecular weight of two or morekinds of structural isomers included in this mixture.

GPC device: HLC-8220 (manufactured by Tosoh Corporation)

Guard column: TSK guard column Super HZM-H

Column: TSK gel Super HZ 2000, TSK gel Super HZ 4000, TSK gel Super HZ-M(manufactured by Tosoh Corporation, 4.6 mm (inner diameter)×15.0 cm,three types of columns are connected in series)

Eluent: Tetrahydrofuran (THF), containing a stabilizer(2,6-di-t-butyl-4-methylphenol)

Flow rate of eluent: 0.35 mL/min

Column temperature: 40° C.

Inlet temperature: 40° C.

Refractive index (RI) measurement temperature: 40° C.

Sample concentration: 0.3 mass %

Sample introduction amount: 10 μL

Synthesis Method

The compound represented by General Formula 1 described above can besynthesized by a well-known method. As an example of the synthesismethod, a method of allowing a reaction such as a ring-opening additionreaction between the carboxylic acid anhydride and a compoundrepresented by the following General Formula 2 can be used, for example.In General Formula 2, R, X, L, and m are the same as those in GeneralFormula 1. A represents a hydrogen atom, an alkali metal atom, orquaternary ammonium base and is preferably a hydrogen atom.

In a case of using a butanetetracarboxylic acid anhydride, for example,the reaction between the carboxylic acid anhydride and a compoundrepresented by General Formula 2 is performed by mixing thebutanetetracarboxylic acid anhydride at a percentage of 0.4 to 0.5 moleswith respect to 1 equivalent of a hydroxyl group, and heating andstirring the mixture approximately for 3 to 12 hours, under the absenceof solvent, if necessary, under the presence of an organic solventhaving a boiling point equal to or higher than 50° C., further, acatalyst such as tertiary amine or inorganic base. Even in a case ofusing other carboxylic acid anhydride, a reaction between the carboxylicacid anhydride and the compound represented by General Formula 2 can beperformed under the reaction conditions described above or underwell-known reaction conditions.

After the reaction, post-process such as purification may be performed,if necessary.

In addition, the compound represented by General Formula 2 can also beobtained by using a commercially available product or by a well-knownpolyester synthesis method. For example, as the polyester synthesismethod, ring-opening polymerization of lactone can be used. As thering-opening polymerization of lactone, descriptions disclosed inparagraphs 0050 to 0051 of JP2016-071926A can be referred to. However,the compound represented by General Formula 2 is not limited to acompound obtained by the ring-opening polymerization of lactone, and canalso be a compound obtained by a well-known polyester synthesis method,for example, polycondensation of polyvalent carboxylic acid andpolyhydric alcohol or polycondensation of hydroxycarboxylic acid.

The synthesis method described above is merely an example and there isno limitation regarding the synthesis method of the compound representedby General Formula 1. Any well-known synthesis method can be usedwithout limitation, as long as it is a method capable of synthesizingthe compound represented by General Formula 1. The reaction productafter the synthesis can be used for forming the magnetic layer, as itis, or by purifying the reaction product by a well-known method, ifnecessary. The compound represented by General Formula 1 may be usedalone or in combination of two or more kinds having differentstructures, in order to form the magnetic layer. In addition, thecompound represented by General Formula 1 may be used as a mixture oftwo or more kinds of structural isomers. For example, in a case ofobtaining two or more kinds of structural isomers by the synthesisreaction of the compound represented by General Formula 1, the mixturecan also be used for forming the magnetic layer.

As the compound represented by General Formula 1, various compoundsincluded in reaction products shown in synthesis examples in Examplesdisclosed in JP2016-071926A can be used. For example, as a specificexample thereof, compounds shown in the following Table 1 can be used. Aweight-average molecular weight shown in Table 1 is a weight-averagemolecular weight of the compound represented by structural formula shownin Table 1 or a weight-average molecular weight of the compoundrepresented by structural formula shown in Table 1 and a mixture ofstructural isomers thereof.

TABLE 1 Weight- average molecular Types Structural Formula weight Com-pound 1

9200 Com- pound 2

6300 Com- pound 3

5300 Com- pound 4

8000 Com- pound 5

8700 Com- pound 6

8600 Com- pound 7

6200 Com- pound 8

8000

As an aspect of a preferred example of the compound having the partialstructure and the adsorption part represented by General Formula A, apolyalkyleneimine derivative including a polyester chain represented bythe following Formula 2-A or 2-B as General Formula A is used.Hereinafter, the polyalkyleneimine derivative will be described.

Polyalkyleneimine Derivative

The polyalkyleneimine derivative is a compound including at least onepolyester chain selected from the group consisting of a polyester chainrepresented by the following Formula 2-A and a polyester chainrepresented by the following Formula 2-B, and a polyalkyleneimine chainhaving a number average molecular weight of 300 to 3,000. A percentageof the polyalkyleneimine chain occupying the compound is preferablysmaller than 5.0 mass %.

The polyalkyleneimine derivative includes a polyalkyleneimine chainwhich is an aspect of the adsorption part described above. In addition,it is thought that, the steric hindrance caused by the polyester chainincluded in the polyalkyleneimine derivative is caused in the magneticlayer forming composition and/or the magnetic solution, and accordingly,it is possible to prevent aggregation of the hexagonal ferriteparticles.

Hereinafter, the polyester chain and the polyalkyleneimine chainincluded in the polyalkyleneimine derivative will be described.

Polyester Chain

Structure of Polyester Chain

The polyalkyleneimine derivative includes at least one polyester chainselected from the group consisting of a polyester chain represented bythe following Formula 2-A and a polyester chain represented by thefollowing Formula 2-B, together with a polyalkyleneimine chain whichwill be described later. In one aspect, the polyester chain is bonded toan alkyleneimine chain represented by Formula A which will be describedlater by a nitrogen atom N included in Formula A and a carbonyl bond—(C═O)— at *¹ of Formula A, and —N—(C═O)— can be formed. In addition, inanother aspect, an alkyleneimine chain represented by Formula B whichwill be described later and the polyester chain can form a saltcrosslinking group by a nitrogen cation N⁺ in Formula B and an anionicgroup including a polyester chain. As the salt crosslinking group, acomponent formed by an oxygen anion O⁻ included in the polyester chainand N⁺ in Formula B can be used.

As the polyester chain bonded to the alkyleneimine chain represented byFormula A by a nitrogen atom N included in Formula A and a carbonyl bond—(C═O)—, the polyester chain represented by Formula 2-A can be used. Thepolyester chain represented by Formula 2-A can be bonded to thealkyleneimine chain represented by Formula A by forming —N—(C═O)— by anitrogen atom included in the alkyleneimine chain and a carbonyl group—(C═O)— included in the polyester chain at the bonding site representedby *¹.

In addition, as the polyester chain bonded to the alkyleneimine chainrepresented by Formula B by forming a salt crosslinking group by N⁺ inFormula B and an anionic group including the polyester chain, thepolyester chain represented by Formula 2-B can be used. The polyesterchain represented by Formula 2-B can form N⁺ in Formula B and a saltcrosslinking group by an oxygen anion O⁻.

L¹ in Formula 2-A and L² in Formula 2-B each independently represent adivalent linking group. As the divalent linking group, an alkylene grouphaving 3 to 30 carbon atoms can be preferably used. In a case where thealkylene group includes a substituent, the number of carbon atoms of thealkylene group is the number of carbon atoms of a part (main chain part)excluding the substituent, as described above.

b11 in Formula 2-A and b21 Formula 2-B each independently represent aninteger equal to or greater than 2, for example, an integer equal to orsmaller than 200. The number of lactone repeating units shown in Table 3which will be described later corresponds to b11 in Formula 2-A or b21Formula 2-B.

b12 in Formula 2-A and b22 Formula 2-B each independently represent 0 or1.

X¹ in Formula 2-A and X² Formula 2-B each independently represent ahydrogen atom or a monovalent substituent. As the monovalentsubstituent, a monovalent substituent selected from the group consistingof an alkyl group, a haloalkyl group (for example, fluoroalkyl group),an alkoxy group, a polyalkyleneoxyalkyl group, and an aryl group can beused.

The alkyl group may include a substituent or may be non-substituted. Asthe alkyl group including a substituent, an alkyl group (hydroxyalkylgroup) substituted with a hydroxyl group, and an alkyl group substitutedwith one or more halogen atoms are preferable. In addition, an alkylgroup (haloalkyl group) in which all of hydrogen atoms bonded to carbonatoms are substituted with halogen atoms is also preferable. As thehalogen atom, a fluorine atom, a chlorine atom, or a bromine atom can beused. The alkyl group is more preferably an alkyl group having 1 to 30carbon atoms, and even more preferably an alkyl group having 1 to 10carbon atoms. The alkyl group may have any of a linear, branched, andcyclic structure. The same applies to the haloalkyl group.

Specific examples of substituted or non-substituted alkyl group orhaloalkyl group include a methyl group, an ethyl group, a propyl group,a butyl group, a pentyl group, a hexyl group, a heptyl group, an octylgroup, a nonyl group, a decyl group, a undecyl group, a dodecyl group, atridecyl group, a pentadecyl group, a hexadecyl group, a heptadecylgroup, an octadecyl group, an eicosyl group, an isopropyl group, anisobutyl group, an isopentyl group, a 2-ethylhexyl group, a tert-octylgroup, a 2-hexyldecyl group, a cyclohexyl group, a cyclopentyl group, acyclohexylmethyl group, an octylcyclohexyl group, a 2-norbornyl group, a2,2,4-trimethylpentyl group, an acetylmethyl group, an acetylethylgroup, a hydroxymethyl group, a hydroxyethyl group, a hydroxypropylgroup, a hydroxybutyl group, a hydroxypentyl group, a hydroxyhexylgroup, a hydroxyheptyl group, a hydroxyoctyl group, a hydroxynonylgroup, a hydroxydecyl group, a chloromethyl group, a dichloromethylgroup, a trichloromethyl group, a bromomethyl group, a1,1,1,3,3,3-hexafluoroisopropyl group, a heptafluoropropyl group, apentadecafluoroheptyl group, a nonadecafluorononyl group, ahydroxyundecyl group, a hydroxydodecyl group, a hydroxypentadecyl group,a hydroxyheptadecyl group, and a hydroxyoctadecyl group.

Examples of the alkoxy group include a methoxy group, an ethoxy group, apropyloxy group, a hexyloxy group, a methoxyethoxy group, amethoxyethoxyethoxy group, and a methoxyethoxyethoxymethyl group.

The polyalkyleneoxyalkyl group is a monovalent substituent representedby R¹⁰(OR¹¹)n1(O)m1-. R¹⁰ represents an alkyl group, R¹¹ represents analkylene group, n1 represents an integer equal to or greater than 2, andm1 represents 0 or 1.

The alkyl group represented by R¹⁰ is as described regarding the alkylgroup represented by X¹ or X². For the specific description of thealkylene group represented by R¹¹, the description regarding the alkylgroup represented by X¹ or X² can be applied by replacing the alkylgroup with an alkylene group obtained by removing one hydrogen atom fromthe alkylene group (for example, by replacing the methyl group with amethylene group). n1 is an integer equal to or greater than 2, forexample, is an integer equal to or smaller than 10, and is preferably aninteger equal to or smaller than 5.

The aryl group may include a substituent or may be annelated, and morepreferably an aryl group having 6 to 24 carbon atoms, and examplesthereof include a phenyl group, a 4-methylphenyl group, 4-phenylbenzoicacid, a 3-cyanophenyl group, a 2-chlorophenyl group, and a 2-naphthylgroup.

The polyester chain represented by Formula 2-A and the polyester chainrepresented by Formula 2-B can have a polyester-derived structureobtained by a well-known polyester synthesis method. As the polyestersynthesis method, ring-opening polymerization of lactone disclosed inparagraphs 0056 and 0057 of JP2015-28830A can be used. However, thestructure of the polyester chain is not limited to the polyester-derivedstructure obtained by the ring-opening polymerization of lactone, andcan be a polyester-derived structure obtained by a well-known polyestersynthesis method, for example, polycondensation of polyvalent carboxylicacid and polyhydric alcohol or polycondensation of hydroxycarboxylicacid.

Number Average Molecular Weight of Polyester Chain

A number average molecular weight of the polyester chain is preferablyequal to or greater than 200, more preferably equal to or greater than400, and even more preferably equal to or greater than 500, from aviewpoint of improvement of dispersibility of ferromagnetic hexagonalferrite powder. In addition, from the same viewpoint, the number averagemolecular weight of the polyester chain is preferably equal to orsmaller than 100,000 and more preferably equal to or smaller than50,000. As described above, it is considered that the polyester chainfunctions to cause steric hindrance in the magnetic layer formingcomposition and/or the magnetic solution and preventing the aggregationof the hexagonal ferrite particles. It is assumed that the polyesterchain having the number average molecular weight described above canexhibit such an operation in an excellent manner. The number averagemolecular weight of the polyester chain is a value obtained byperforming reference polystyrene conversion of a value measured by GPC,regarding polyester obtained by hydrolysis of a polyalkyleneiminederivative. The value acquired as described above is the same as a valueobtained by performing reference polystyrene conversion of a valuemeasured by GPC regarding polyester used for synthesis of thepolyalkyleneimine derivative. Accordingly, the number average molecularweight acquired regarding polyester used for synthesis of thepolyalkyleneimine derivative can be used as the number average molecularweight of the polyester chain included in the polyalkyleneiminederivative. For the measurement conditions of the number averagemolecular weight of the polyester chain, the measurement conditions ofthe number average molecular weight of polyester in a specific examplewhich will be described later can be referred to.

Polyalkyleneimine Chain

Number Average Molecular Weight

The number average molecular weight of the polyalkyleneimine chainincluded in the polyalkyleneimine derivative is a value obtained byperforming reference polystyrene conversion of a value measured by GPC,regarding polyalkyleneimine obtained by hydrolysis of apolyalkyleneimine derivative. The value acquired as described above isthe same as a value obtained by performing reference polystyreneconversion of a value measured by GPC regarding polyalkyleneimine usedfor synthesis of the polyalkyleneimine derivative. Accordingly, thenumber average molecular weight acquired regarding polyalkyleneimineused for synthesis of the polyalkyleneimine derivative can be used asthe number average molecular weight of the polyalkyleneimine chainincluded in the polyalkyleneimine derivative. For the measurementconditions of the number average molecular weight of thepolyalkyleneimine chain, a specific example which will be describedlater can be referred to. In addition, the polyalkyleneimine is apolymer which can be obtained by ring-opening polymerization ofalkyleneimine. In the polyalkyleneimine derivative, the term “polymer”is used to include a homopolymer including a repeating unit in the samestructure and a copolymer including a repeating unit in two or morekinds of different structures.

The hydrolysis of the polyalkyleneimine derivative can be performed byvarious methods which are normally used as a hydrolysis method of ester.For details of such a method, description of a hydrolysis methoddisclosed in “The Fifth Series of Experimental Chemistry Vol. 14Synthesis of Organic Compounds II—Alcohol•Amine” (Chemical Society ofJapan, Maruzen Publication, issued August, 2005) pp. 95 to 98, anddescription of a hydrolysis method disclosed in “The Fifth Series ofExperimental Chemistry Vol. 16 Synthesis of Organic CompoundsIV—Carboxylic acid•Amino Acid•Peptide” (Chemical Society of Japan,Maruzen Publication, issued March, 2005) pp. 10 to 15 cam be referredto, for example.

The polyalkyleneimine is decomposed from the obtained hydrolyzate bywell-known separating means such as liquid chromatography, and thenumber average molecular weight thereof can be acquired.

The number average molecular weight of the polyalkyleneimine chainincluded in the polyalkyleneimine derivative is in a range of 300 to3,000. The inventors have surmised that when the number averagemolecular weight of the polyalkyleneimine chain is in the rangedescribed above, the polyalkyleneimine derivative can be effectivelyadsorbed to the surface of the hexagonal ferrite particles. The numberaverage molecular weight of the polyalkyleneimine chain is preferablyequal to or greater than 500, from a viewpoint of adsorption propertiesto the surface of the hexagonal ferrite particles. From the sameviewpoint, the number average molecular weight is preferably equal to orsmaller than 2,000.

Percentage of Polyalkyleneimine Chain Occupying PolyalkyleneimineDerivative

As described above, the inventors have considered that thepolyalkyleneimine chain included in the polyalkyleneimine derivative canfunction as an adsorption part to the surface of the hexagonal ferriteparticles. A percentage of the polyalkyleneimine chain occupying thepolyalkyleneimine derivative (hereinafter, also referred to as a“polyalkyleneimine chain percentage”) is preferably smaller than 5.0mass %, from a viewpoint of increasing the dispersibility of theferromagnetic hexagonal ferrite powder. From a viewpoint of improvingthe dispersibility of the ferromagnetic hexagonal ferrite powder, thepolyalkyleneimine chain percentage is more preferably equal to orsmaller than 4.9 mass %, even more preferably equal to or smaller than4.8 mass %, further more preferably equal to or smaller than 4.5 mass %,still more preferably equal to or smaller than 4.0 mass %, and stilleven more preferably equal to or smaller than 3.0 mass %. In addition,from a viewpoint of improving the dispersibility of the ferromagnetichexagonal ferrite powder, the polyalkyleneimine chain percentage ispreferably equal to or greater than 0.2 mass %, more preferably equal toor greater than 0.3 mass %, and even more preferably equal to or greaterthan 0.5 mass %.

The percentage of the polyalkyleneimine chain described above can becontrolled, for example, according to a mixing ratio ofpolyalkyleneimine and polyester used at the time of synthesis.

The percentage of the polyalkyleneimine chain occupying thepolyalkyleneimine derivative can be calculated from an analysis resultobtained by element analysis such as nuclear magnetic resonance (NMR),more specifically, ¹H-NMR and ¹³C-NMR, and a well-known method. Thevalue calculated as described is the same as a theoretical valueacquired from a compounding ratio of a synthesis raw material in thepolyalkyleneimine derivative, and thus, the theoretical value acquiredfrom the compounding ratio can be used as the percentage of thepolyalkyleneimine chain occupying the polyalkyleneimine derivative.

Structure of Polyalkyleneimine Chain

The polyalkyleneimine chain has a polymer structure including the sameor two or more different alkyleneimine chains. As the alkyleneiminechain included, an alkyleneimine chain represented by the followingFormula A and an alkyleneimine chain represented by Formula B can beused. In the alkyleneimine chains represented by the following Formulae,the alkyleneimine chain represented by Formula A can include a bondingsite with a polyester chain. In addition, the alkyleneimine chainrepresented by Formula B can be bonded to a polyester chain by the saltcrosslinking group described above. The polyalkyleneimine derivative canhave a structure in which one or more polyester chains are bonded to thepolyalkyleneimine chain, by including one or more alkyleneimine chains.In addition, the polyalkyleneimine chain may be formed of only a linearstructure or may have a branched tertiary amine structure. It ispreferable that the polyalkyleneimine chain has a branched structure,from a viewpoint of further improving the dispersibility. As a componenthaving a branched structure, a component bonded to an adjacentalkyleneimine chain at *¹ in the following Formula A and a componentbonded to an adjacent alkyleneimine chain at *² in the following FormulaB can be used.

In Formula A, R¹ and R² each independently represent a hydrogen atom oran alkyl group, a1 represents an integer equal to or greater than 2, and*¹ represents a bonding site with a polyester chain, an adjacentalkyleneimine chain, a hydrogen atom, or a substituent.

In Formula B, R³ and R⁴ each independently represent a hydrogen atom oran alkyl group, and a2 represents an integer equal to or greater than 2.The alkyleneimine chain represented by Formula B is bonded to apolyester chain including an anionic group by forming a saltcrosslinking group by N⁺ in Formula B and an anionic group included inthe polyester chain.

* in Formula A and Formula B and *² in Formula B each independentlyrepresent a site to be bonded to an adjacent alkyleneimine chain, ahydrogen atom, or a substituent.

Hereinafter, Formula A and Formula B will be further described indetail.

R¹ and R² in Formula A and R³ and R⁴ in Formula B each independentlyrepresent a hydrogen atom or an alkyl group. As the alkyl group, forexample, an alkyl group having 1 to 6 carbon atoms can be used, and thealkyl group is preferably an alkyl group having 1 to 3 carbon atoms,more preferably a methyl group or an ethyl group, and even morepreferably a methyl group. As an aspect of a combination of R¹ and R² inFormula A, an aspect in which one is a hydrogen atom and the other is analkyl group, an aspect in which both of them are hydrogen atoms, and anaspect in which both of them are alkyl groups (alkyl groups which arethe same as each other or different from each other) are used, and theaspect in which both of them are hydrogen atoms is preferably used. Thepoint described above is also applied to R³ and R⁴ in Formula B in thesame manner.

Ethyleneimine has a structure having the minimum number of carbon atomsconfiguring a ring as alkyleneimine, and the number of carbon atoms of amain chain of the alkyleneimine chain (ethyleneimine chain) obtained byring opening of ethyleneimine is 2. Accordingly, the lower limit of a1in Formula A and a2 in Formula B is 2. That is, a1 in Formula A and a2in Formula B each independently represent an integer equal to or greaterthan 2. a1 in Formula A and a2 in Formula B are each independentlypreferably equal to or smaller than 10, more preferably equal to orsmaller than 6, even more preferably equal to or smaller than 4, stillmore preferably 2 or 3, and still even more preferably 2, from aviewpoint of adsorption properties to the surface of the particles ofthe ferromagnetic powder.

The details of the bonding between the alkyleneimine chain representedby Formula A or the alkyleneimine chain represented by Formula B and thepolyester chain are as described above.

Each alkyleneimine chain is bonded to an adjacent alkyleneimine chain, ahydrogen atom, or a substituent, at a position represented by * in eachFormula. As the substituent, for example, a monovalent substituent suchas an alkyl group (for example, an alkyl group having 1 to 6 carbonatoms) can be used, but there is no limitation. In addition, thepolyester chain may be bonded as the substituent.

Weight-Average Molecular Weight of Polyalkyleneimine Derivative

A molecular weight of the polyalkyleneimine derivative is preferably1,000 to 80,000 as the weight-average molecular weight as describedabove. The weight-average molecular weight of the polyalkyleneiminederivative is more preferably equal to or greater than 1,500, even morepreferably equal to or greater than 2,000, and further more preferablyequal to or greater than 3,000. In addition, the weight-averagemolecular weight of the polyalkyleneimine derivative is more preferablyequal to or smaller than 60,000, even more preferably equal to orsmaller than 40,000, and further more preferably equal to or smallerthan 35,000, and still more preferably equal to or smaller than 34,000.For measurement conditions of the weight-average molecular weight of thepolyalkyleneimine derivative, a specific example which will be describedlater can be referred to.

Synthesis Method

The synthesis method is not particularly limited, as long as thepolyalkyleneimine derivative includes the polyester chain and thepolyalkyleneimine chain having a number average molecular weight of 300to 3,000 at the ratio described above. As a preferred aspect of thesynthesis method, descriptions disclosed in paragraphs 0061 to 0069 ofJP2015-28830A can be referred to.

As a specific example of the polyalkyleneimine derivative, variouspolyalkyleneimine derivatives shown in Table 2 synthesized by usingpolyethyleneimine and polyester shown in Table 2 can be used. For thedetails of the synthesis reaction, descriptions disclosed in Exampleswhich will be described later and/or Examples of JP2015-28830A can bereferred to.

TABLE 2 Percentage of Polyalkyleneimine chain Weight- PolyalkyleneiminePolyethyleneimine (polyethyleneimine Amine average (polyethyleneimine)amount chain) Acid value value molecular derivative Polyethyleneimine*(g) (mass %) Polyester (mgKOH/g) (mgKOH/g) weight (J-1) SP-018 5 4.8(i-1) 22.2 28.6 15,000 (J-2) SP-006 2.4 2.3 (i-2) 35 17.4 7,000 (J-3)SP-012 4.5 4.3 (i-3) 6.5 21.2 22,000 (J-4) SP-006 5 4.8 (i-4) 4.9 11.834,000 (J-5) SP-003 5 4.8 (i-5) 10.1 15.2 19,000 (J-6) SP-018 1.2 1.2(i-6) 68.5 22.4 8,000 (J-7) SP-018 3 2.9 (i-7) 39.9 16.8 13,000 (J-8)SP-012 2.5 2.4 (i-8) 15.5 18.9 18,000 (J-9) SP-006 5 4.8 (i-9) 11.1 16.822,000 (J-10) SP-003 4 3.8 (i-10) 4.4 14.1 24,000 (J-11) SP-012 0.3 0.3(i-10) 8.1 7.8 28,000 (J-12) SP-018 1 1 (i-1) 28.8 6.7 15,000 (J-13)SP-012 5 4.8 (i-6) 61 28.2 4,000 (J-14) SP-006 2.4 2.3 (i-11) 30 17.46,000 (J-15) SP-006 2.4 2.3 (i-12) 42.8 18.1 6,300 (J-16) SP-006 2.4 2.3(i-13) 43.7 17.9 5,900 (J-17) SP-006 2.4 2.3 (i-14) 42.5 17.1 5,300(J-18) SP-006 2.3 2.4 (i-15) 37.5 19.4 7,300 (J-19) SP-006 2.3 2.4(i-16) 24.6 16 9,800 (J-20) SP-006 2.3 2.4 (i-17) 27.5 26.1 9,300 (J-21)SP-006 2.3 2.4 (i-18) 31.7 8.9 8,900 (J-22) SP-006 2.3 2.4 (i-19) 15.313.9 15,100 (J-23) SP-006 2.3 2.4 (i-20) 38.1 22.4 7,580 (*Note)Polyethyleneimine shown in Table 2 is as described below SP-003(Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd.) numberaverage molecular weight of 300) SP-006 (Polyethyleneimine (manufacturedby Nippon Shokubai Co., Ltd.) number average molecular weight of 600)SP-012 (Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd.)number average molecular weight of 1,200) SP-018 (Polyethyleneimine(manufactured by Nippon Shokubai Co., Ltd.) number average molecularweight of 1,800)

The polyester shown in Table 2 is polyester synthesized by thering-opening polymerization of lactone by using lactone and anucleophilic reagent (carboxylic acid) shown in Table 3. For the detailsof the synthesis reaction, descriptions disclosed in Examples which willbe described later and/or Examples of JP2015-28830A can be referred to.

TABLE 3 Number Amount of Weight-average average carboxylic acidmolecular molecular Number of lactone repeating Polyester Carboxylicacid (g) Lactone weight weight units (i-1) n-Octanoic acid 12.6ε-Caprolactone 9,000 7,500 20 (i-2) n-Octanoic acid 16.8 ε-Caprolactone7,000 5,800 15 (i-3) n-Octanoic acid 3.3 L-Lactide 22,000 18,000 60(i-4) Palmitic acid 4.5 ε-Caprolactone 38,000 31,000 100 (i-5) Palmiticacid 12.8 δ-Valerolactone 16,000 13,000 40 (i-6) Stearic acid 99.7ε-Caprolactone 2,500 2,000 5 (i-7) Glycol acid 13.3 ε-Caprolactone 4,8004,000 10 (i-8) 12-Hydroxystearic acid 20 δ-Valerolactone 13,000 10,00030 (i-9) 12-Hydroxystearic acid 13.2 ε-Caprolactone 17,000 14,000 40(i-10) 2-Naphthoic acid 3.8 ε-Caprolactone 27,000 22,500 80 (i-11)[2-(2-Methoxyethoxy)ethoxy] acetic acid 15.6 ε-Caprolactone 8,700 6,30015 (i-12) n-Octanoic acid 16.8 Lactide 8,100 4,100 15 (i-13) n-Octanoicacid 17.31 L-Lactide 6,900 3,500 10 (L-Lactide derived) ε-Caprolactone 5(ε-Caprolactone derived) (i-14) n-Octanoic acid 17.31 L-Lactide 6,2003,200 5 (L-Lactide derived) ε-Caprolactone 10 (ε-Caprolactone derived)(i-15) Nonafluorovaleric acid 30.8 ε-Caprolactone 9,000 7,500 15 (i-16)Heptadecafluorononanoic acid 54.2 ε-Caprolactone 8,000 5,000 15 (i-17)3,5,5-Trimethylhexanoic acid 18.5 ε-Caprolactone 10,000 5,800 15 (i-18)4-Oxovaleric acid 13.6 ε-Caprolactone 7,400 4,100 15 (i-19)[2-(2-Methoxyethoxy)ethoxy] acetic acid 20.8 ε-Caprolactone 15,30011,500 30 (i-20) Benzoic acid 14.3 ε-Caprolactone 7,000 3,000 15

The acid value and amine value described above are determined by apotentiometric method (solvent: tetrahydrofuran/water=100/10 (volumeratio), titrant: 0.01 N (0.01 mol/l), sodium hydroxide aqueous solution(acid value), 0.01 N (0.01 mol/l) hydrochloric acid (amine value)).

The average molecular weight (number average molecular weight andweight-average molecular weight) is acquired by performing referencepolystyrene conversion of a value measured by GPC.

Specific examples of the measurement conditions of the average molecularweights of polyester, polyalkyleneimine, and a polyalkyleneiminederivative are respectively as described below.

Measurement Conditions of Average Molecular Weight of Polyester

Measurement device: HLC-8220 GPC (manufactured by Tosoh Corporation)

Column: TSK gel Super HZ2000/TSK gel Super HZ 4000/TSK gel Super HZ-H(manufactured by Tosoh Corporation)

Eluent: Tetrahydrofuran (THF)

Flow rate: 0.35 mL/min

Column temperature: 40° C.

Detector: differential refractometry (RI) detector

Measurement Conditions of Average Molecular Weight of Polyalkyleneimineand Average Molecular Weight of Polyalkyleneimine Derivative

Measurement device: HLC-8320 GPC (manufactured by Tosoh Corporation)

Column: three TSK gel Super AWM-H (manufactured by Tosoh Corporation)

Eluent: N-methyl-2-pyrrolidone (10 mmol/l of lithium bromide is added asan additive)

Flow rate: 0.35 mL/min

Column temperature: 40° C.

Detector: differential refractometry (RI) detector

The dispersing agent described above is mixed with ferromagnetichexagonal ferrite powder, a binder, an abrasive, and a solvent, andthus, the magnetic layer forming composition can be prepared. Inaddition, the magnetic layer of the magnetic tape can include thedispersing agent, together with the ferromagnetic hexagonal ferritepowder, the binder, and the abrasive. The dispersing agent may be usedalone or in combination of two or more kinds having differentstructures. In a case of using two more kinds thereof in combination,the content thereof means the total content of the compounds used incombination. The point described above is also applied to the content ofvarious components disclosed in the specification.

The content of the dispersing agent is preferably 0.5 to 25.0 parts bymass with respect to 100.0 parts by mass of the ferromagnetic hexagonalferrite powder. The content of the dispersing agent is preferably equalto or greater than 0.5 parts by mass, more preferably equal to orgreater than 1.0 part by mass, even more preferably equal to or greaterthan 5.0 parts by mass, and still more preferably equal to or greaterthan 10.0 parts by mass, with respect to 100.0 parts by mass of theferromagnetic hexagonal ferrite powder, from viewpoints of improving thedispersibility of the ferromagnetic hexagonal ferrite powder and thedurability of the magnetic layer. Meanwhile, it is preferable toincrease the filling percentage of the ferromagnetic hexagonal ferritepowder of the magnetic layer, in order to improve recording density.From this point, it is preferable that the content of the componentsother than the ferromagnetic hexagonal ferrite powder is relatively low.From the viewpoints described above, the content of the dispersing agentis preferably equal to or smaller than 25.0 parts by mass, morepreferably equal to or smaller than 20.0 parts by mass, even morepreferably equal to or smaller than 18.0 parts by mass, and still morepreferably equal to or smaller than 15.0 parts by mass with respect to100.0 parts by mass of the ferromagnetic hexagonal ferrite powder.

Hereinafter, the magnetic tape will be further described in detail.

Magnetic Layer

Ferromagnetic Powder

The magnetic layer includes ferromagnetic hexagonal ferrite powder asthe ferromagnetic powder. As an index of a particle size of theferromagnetic hexagonal ferrite powder, an activation volume can beused. The “activation volume” is a unit of magnetization reversal.Regarding the activation volume described in the invention and thespecification, magnetic field sweep rates of a coercivity He measurementpart at time points of 3 minutes and 30 minutes are measured by using anoscillation sample type magnetic-flux meter, and the activation volumeis a value acquired from the following relational expression of Hc andan activation volume V.

Hc=2Ku/Ms{1−[(kT/KuV)ln(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant, Ms: saturationmagnetization, k: Boltzmann's constant, T: absolute temperature, V:activation volume, A: spin precession frequency, and t: magnetic fieldreversal time]

It is desired that recording density is increased (high-densityrecording is realized) in the magnetic tape, in accordance with a greatincrease in information content of recent years. As a method forachieving high-density recording, a method of decreasing a particle sizeof ferromagnetic powder included in a magnetic layer and increasing afilling percentage of the ferromagnetic powder of the magnetic layer isused. From this viewpoint, the activation volume of the ferromagnetichexagonal ferrite powder is preferably equal to or smaller than 2,500nm³, more preferably equal to or smaller than 2,300 nm³, and even morepreferably equal to or smaller than 2,000 nm³. Meanwhile, from aviewpoint of stability of magnetization, the activation volume is, forexample, preferably equal to or greater than 800 nm³, more preferablyequal to or greater than 1,000 nm³, and even more preferably equal to orgreater than 1,200 nm³. A percentage of the hexagonal ferrite particleshaving the aspect ratio and the length in the long axis directiondescribed above in all of the hexagonal ferrite particles observed inthe STEM image, can be, for example, equal to or greater than 50%, as apercentage with respect to all of the hexagonal ferrite particlesobserved in the STEM image, based on the particle number. In addition,the percentage can be, for example, equal to or smaller than 95% and canexceed 95%. For other details of ferromagnetic hexagonal ferrite powder,for example, descriptions disclosed in paragraphs 0012 to 0030 ofJP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, andparagraphs 0013 to 0030 of JP2012-204726A can be referred to.

The content (filling percentage) of the ferromagnetic hexagonal ferritepowder of the magnetic layer is preferably in a range of 50 to 90 mass %and more preferably in a range of 60 to 90 mass %. The component otherthan the ferromagnetic hexagonal ferrite powder of the magnetic layer isat least a binder and an abrasive, and arbitrarily one or more kinds ofother additives can be included. The high filling percentage of theferromagnetic hexagonal ferrite powder of the magnetic layer ispreferable, from a viewpoint of improving recording density.

Binder

The magnetic tape includes a binder in the magnetic layer together withthe ferromagnetic hexagonal ferrite powder. The binder is one or morekinds of resin. For example, as the binder, a resin selected from apolyurethane resin, a polyester resin, a polyamide resin, a vinylchloride resin, an acrylic resin obtained by copolymerizing styrene,acrylonitrile, or methyl methacrylate, a cellulose resin such asnitrocellulose, an epoxy resin, a phenoxy resin, and a polyvinylalkylalresin such as polyvinyl acetal or polyvinyl butyral can be used alone ora plurality of resins can be mixed with each other to be used. Amongthese, a polyurethane resin, an acrylic resin, a cellulose resin, and avinyl chloride resin are preferable. These resins may be homopolymers orcopolymers. These resins can be used as the binder even in thenon-magnetic layer and/or a back coating layer which will be describedlater. For the binder described above, description disclosed inparagraphs 0028 to 0031 of JP2010-24113A can be referred to. Inaddition, the binder may be a radiation curable resin such as anelectron beam-curable resin. For the radiation curable resin,descriptions disclosed in paragraphs 0044 and 0045 of JP2011-48878A canbe referred to.

In addition, a curing agent can be used together with a resin which canbe used as the binder. The curing agent is a compound including at leastone and preferably two or more crosslinking functional groups in onemolecule. At least a part of the curing agent is included in themagnetic layer in a state of being reacted (crosslinked) with othercomponents such as the binder, by proceeding the curing reaction in themagnetic layer forming step. As the curing agent, polyisocyanate issuitable. For the details of polyisocyanate, descriptions disclosed inparagraphs 0124 and 0125 of JP2011-216149A can be referred to. Theamount of the curing agent used can be, for example, 0 to 80.0 parts bymass with respect to 100.0 parts by mass of the binder, and ispreferably 50.0 to 80.0 parts by mass, from a viewpoint of improvementof strength of each layer such as the magnetic layer.

Abrasive

The magnetic tape includes an abrasive in the magnetic layer. Theabrasive means non-magnetic powder having Mohs hardness exceeding 8 andis preferably non-magnetic powder having Mohs hardness equal to orgreater than 9. The abrasive may be powder of inorganic substances(inorganic powder), may be powder of organic substances (organicpowder), and the inorganic powder is preferable. The abrasive is morepreferably inorganic powder having Mohs hardness exceeding 8 and evenmore preferably inorganic powder having Mohs hardness equal to orgreater than 9. A maximum value of Mohs hardness is 10 of diamond.Specifically, powders of alumina (Al₂O₃), silicon carbide, boron carbide(B₄C), TiC, cerium oxide, zirconium oxide (ZrO₂), diamond, and the likecan be used as the abrasive, and among these, alumina powder ispreferable. For the alumina powder, a description disclosed in aparagraph 0021 of JP2013-229090A can be referred to. In addition, aspecific surface area can be used as an index of a particle size of theabrasive. A great value of the specific surface area means a smallparticle size. From a viewpoint of decreasing the magnetic layer surfaceRa, an abrasive having a specific surface area measured byBrunauer-Emmett-Teller (BET) method (hereinafter, referred to as a “BETspecific surface area”) which is equal to or greater than 14 m²/g, ispreferably used. In addition, from a viewpoint of dispersibility, anabrasive having a BET specific surface area equal to or smaller than 40m²/g, is preferably used. The content of the abrasive of the magneticlayer is preferably 1.0 to 20.0 parts by mass with respect to 100.0parts by mass of the ferromagnetic powder.

Additives

The magnetic layer includes ferromagnetic hexagonal ferrite powder, abinder, and an abrasive, and may further include one or more kinds ofadditives, if necessary. As the additives, the dispersing agent and thecuring agent described above are used as an example. In addition,examples of the additive which can be included in the magnetic layerinclude a non-magnetic filler, a lubricant, a dispersing agent, adispersing assistant, an antibacterial agent, an antistatic agent, anantioxidant, and carbon black. The non-magnetic filler is identical tothe non-magnetic powder. As the non-magnetic filler, a non-magneticfiller (hereinafter, referred to as a “projection formation agent”)which can function as a projection formation agent which formsprojections suitably protruded from the surface of the magnetic layercan be used. The projection formation agent is a component which cancontribute to the control of friction properties of the surface of themagnetic layer. As the projection formation agent, various non-magneticpowders normally used as a projection formation agent can be used. Thesemay be inorganic substances or organic substances. In one aspect, from aviewpoint of homogenization of friction properties, particle sizedistribution of the projection formation agent is not polydispersionhaving a plurality of peaks in the distribution and is preferablymonodisperse showing a single peak. From a viewpoint of availability ofmonodisperse particles, the projection formation agent is preferablypowder of inorganic substances (inorganic powder). Examples of theinorganic powder include powder of metal oxide, metal carbonate, metalsulfate, metal nitride, metal carbide, and metal sulfide, and powder ofinorganic oxide is preferable. The projection formation agent is morepreferably colloidal particles and even more preferably inorganic oxidecolloidal particles. In addition, from a viewpoint of availability ofmonodisperse particles, the inorganic oxide configuring the inorganicoxide colloidal particles are preferably silicon dioxide (silica). Theinorganic oxide colloidal particles are more preferably colloidal silica(silica colloidal particles). In the invention and the specification,the “colloidal particles” are particles which are not precipitated anddispersed to generate a colloidal dispersion, when 1 g of the particlesis added to 100 mL of at least one organic solvent of at least methylethyl ketone, cyclohexanone, toluene, or ethyl acetate, or a mixedsolvent including two or more kinds of the solvent described above at anarbitrary mixing ratio. In addition, in another aspect, the projectionformation agent is preferably carbon black. An average particle size ofthe projection formation agent is, for example, 30 to 300 nm and ispreferably 40 to 200 nm. In addition, from a viewpoint that theprojection formation agent can exhibit the functions thereof in moreexcellent manner, the content of the projection formation agent of themagnetic layer is preferably 1.0 to 4.0 parts by mass and morepreferably 1.5 to 3.5 parts by mass with respect to 100.0 parts by massof the ferromagnetic powder.

As an example of the additive which can be used in the magnetic layerincluding the abrasive, a dispersing agent disclosed in paragraphs 0012to 0022 of JP2013-131285A can be used as a dispersing agent forimproving dispersibility of the abrasive of the magnetic layer formingcomposition. It is preferable to improve dispersibility of the magneticlayer forming composition such as an abrasive, in order to decrease themagnetic layer surface Ra.

As the additives, a commercially available product or an additiveprepared by a well-known method can be suitably selected and usedaccording to desired properties.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape maydirectly include a magnetic layer on a non-magnetic support, or mayinclude a non-magnetic layer including non-magnetic powder and a binderbetween the non-magnetic support and the magnetic layer. Thenon-magnetic powder used in the non-magnetic layer may be inorganicsubstances or organic substances. In addition, carbon black and the likecan be used. Examples of the inorganic substance include metal, metaloxide, metal carbonate, metal sulfate, metal nitride, metal carbide, andmetal sulfide. These non-magnetic powders can be purchased as acommercially available product or can be manufactured by a well-knownmethod. For details thereof, descriptions disclosed in paragraphs 0146to 0150 of JP2011-216149A can be referred to. For carbon black which canbe used in the non-magnetic layer, descriptions disclosed in paragraphs0040 and 0041 of JP2010-24113A can be referred to. The content (fillingpercentage) of the non-magnetic powder of the non-magnetic layer ispreferably in a range of 50 to 90 mass % and more preferably in a rangeof 60 to 90 mass %.

In regards to other details of a binder or additives of the non-magneticlayer, the well-known technology regarding the non-magnetic layer can beapplied. In addition, in regards to the type and the content of thebinder, and the type and the content of the additive, for example, thewell-known technology regarding the magnetic layer can be applied.

The non-magnetic layer of the invention and the specification alsoincludes a substantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Back Coating Layer

The magnetic tape can also include a back coating layer includingnon-magnetic powder and a binder on a side of the non-magnetic supportopposite to the side including the magnetic layer. The back coatinglayer preferably includes any one or both of carbon black and inorganicpowder. In regards to the binder included in the back coating layer andvarious additives which can be arbitrarily included in the back coatinglayer, a well-known technology regarding the treatment of the magneticlayer and/or the non-magnetic layer can be applied.

Non-Magnetic Support

Next, the non-magnetic support (hereinafter, also simply referred to asa “support”) will be described. As the non-magnetic support, well-knowncomponents such as polyethylene terephthalate, polyethylene naphthalate,polyamide, polyamide imide, aromatic polyamide subjected to biaxialstretching are used. Among these, polyethylene terephthalate,polyethylene naphthalate, and polyamide are preferable. Coronadischarge, plasma treatment, easy-bonding treatment, or thermaltreatment may be performed with respect to these supports in advance.

Total Thickness of Magnetic Tape

The total thickness of the magnetic tape is equal to or smaller than5.30 μm. It is preferable that the total thickness is decreased(thinning), in order to increase the recording capacity per 1 reel of amagnetic tape cartridge. The total thickness of the magnetic tape maybe, for example, equal to or smaller than 5.20 μm, equal to or smallerthan 5.10 μm, or equal to or smaller than 5.00 μm. In addition, thetotal thickness of the magnetic tape is, for example, preferably equalto or greater than 1.00 μm, more preferably equal to or greater than2.00 μm, and even more preferably equal to or greater than 3.00 μm, froma viewpoint of ease of handling (handling properties) of the magnetictape.

Thickness of Non-Magnetic Support and Each Layer

The thickness of the non-magnetic support is preferably 3.00 to 4.50 μm.The thickness of the magnetic layer is preferably equal to or smallerthan 0.15 μm and more preferably equal to or smaller than 0.10 μm, froma viewpoint of realizing recording at high density which is recentlyrequired. The thickness of the magnetic layer is even more preferably ina range of 0.01 to 0.10 μm. The magnetic layer may be at least singlelayer, the magnetic layer may be separated into two or more layershaving different magnetic properties, and a configuration of awell-known multilayered magnetic layer can be applied. A thickness ofthe magnetic layer in a case where the magnetic layer is separated intotwo or more layers is the total thickness of the layers.

The thickness of the non-magnetic layer is, for example, 0.0 to 1.50 μmand is preferably 0.10 to 1.00 μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.90 μm and even more preferably in a range of 0.10 to 0.70 μm.

The thicknesses of various layers of the magnetic tape and thenon-magnetic support can be acquired by a well-known film thicknessmeasurement method. As an example, a cross section of the magnetic tapein a thickness direction is, for example, exposed by a well-known methodof ion beams or microtome, and the exposed cross section is observedwith a scan electron microscope. In the cross section observation,various thicknesses can be acquired as a thickness acquired at oneposition of the cross section in the thickness direction, or anarithmetical mean of thicknesses acquired at a plurality of positions oftwo or more positions, for example, two positions which are arbitrarilyextracted. In addition, the thickness of each layer may be acquired as adesigned thickness calculated according to the manufacturing conditions.

Manufacturing Method

Manufacturing of Magnetic Tape in which Servo Pattern is Formed

Each composition for forming the magnetic layer, the non-magnetic layer,or the back coating layer normally includes a solvent, together withvarious components described above. As the solvent, various organicsolvents generally used for manufacturing a coating type magnetic tapecan be used. The steps of preparing a composition for forming each layergenerally include at least a kneading step, a dispersing step, and amixing step provided before and after these steps, if necessary. Eachstep may be divided into two or more stages. All of raw materials usedin the invention may be added at an initial stage or in a middle stageof each step. In addition, each raw material may be separately added intwo or more steps. In the preparation of the magnetic layer formingcomposition, it is preferable that the abrasive and the ferromagnetichexagonal ferrite powder are separately dispersed as described above. Inorder to manufacture the magnetic tape, a well-known manufacturingtechnology can be used. In the kneading step, an open kneader, acontinuous kneader, a pressure kneader, or a kneader having a strongkneading force such as an extruder is preferably used. The details ofthe kneading processes of these kneaders are disclosed in JP1989-106338A(JP-H01-106338A) and JP1989-79274A (JP-H01-79274A). In addition, inorder to disperse each layer forming composition, glass beads and one ormore kinds of other dispersion beads can be used as a dispersion medium.As such dispersion beads, zirconia beads, titania beads, and steel beadswhich are dispersion beads having high specific gravity are suitable.These dispersion beads are preferably used by optimizing a particlediameter (bead diameter) and a filling percentage of the dispersionbeads. As a dispersion device, a well-known dispersion device can beused. As one of means for obtaining a magnetic tape having cos θ of 0.85to 1.00, a technology of reinforcing the dispersion conditions (forexample, increasing the dispersion time, decreasing the diameter of thedispersion beads used for dispersion and/or increasing the fillingpercentage of the dispersion beads, using the dispersing agent, and thelike) is also preferable. A preferred aspect regarding the reinforcingof the dispersion conditions is as described above. For other details ofthe manufacturing method of the magnetic tape, for example, descriptionsdisclosed in paragraphs 0051 to 0057 of JP2010-24113A can be referredto. For the orientation process, a description disclosed in a paragraph0052 of JP2010-24113A can be referred to. As one of means for obtaininga magnetic tape having cos θ of 0.85 to 1.00, a homeotropic alignmentprocess is preferably performed.

Formation of Servo Pattern

The magnetic tape includes a timing-based servo pattern in the magneticlayer. FIG. 1 shows a disposition example of a region (servo band) inwhich the timing-based servo pattern is formed and a region (data band)interposed between two servo bands. FIG. 2 shows a disposition exampleof the timing-based servo patterns. Here, the disposition example shownin each drawing is merely an example, and the servo pattern, the servobands, and the data bands may be disposed in the disposition accordingto a system of the magnetic tape device (drive). In addition, for theshape and the disposition of the timing-based servo pattern, awell-known technology such as disposition examples shown in FIG. 4, FIG.5, FIG. 6, FIG. 9, FIG. 17, and FIG. 20 of U.S. Pat. No. 5,689,384A canbe applied without any limitation, for example.

The servo pattern can be formed by magnetizing a specific region of themagnetic layer by a servo write head mounted on a servo writer. A regionto be magnetized by the servo write head (position where the servopattern is formed) is determined by standards. As the servo writer, acommercially available servo writer or a servo writer having awell-known configuration can be used. For the configuration of the servowriter, well-known technologies such as technologies disclosed inJP2011-175687A, U.S. Pat. No. 5,689,384A, and U.S. Pat. No. 6,542,325Bcan be referred to without any limitation.

The magnetic tape according to one aspect of the invention describedabove is a magnetic tape in which the total thickness is decreased to beequal to or smaller than 5.30 μm, and the magnetic tape has high surfacesmoothness in which the magnetic layer surface Ra is equal to or smallerthan 1.8 nm and can prevent occurrence of signal defects at the time ofservo signal reproducing in the timing-based servo system.

Magnetic Tape Device

One aspect of the invention relates to a magnetic tape device includingthe magnetic tape, a magnetic head, and a servo head.

The details of the magnetic tape mounted on the magnetic tape device areas described above. Such a magnetic tape includes timing-based servopatterns. Accordingly, a magnetic signal is recorded on the data band bythe magnetic head to form a data track, and/or, when reproducing therecorded signal, a head tracking of a timing-based servo type isperformed based on the read servo pattern, while reading the servopattern by the servo head, and therefore, it is possible to cause themagnetic head to follow the data track at a high accuracy.

As the magnetic head mounted on the magnetic tape device, a well-knownmagnetic head which can perform the recording and/or reproducing of themagnetic signal with respect to the magnetic tape can be used. Arecording head and a reproduction head may be one magnetic head or maybe separated magnetic heads. As the servo head, a well-known servo headwhich can read the timing-based servo pattern of the magnetic tape canbe used. For example, a well-known MR head mounted with a MR element canbe used as the servo head. At least one or two or more servo heads maybe included in the magnetic tape device.

For details of the head tracking of the timing-based servo system, forexample, well-known technologies such as technologies disclosed in U.S.Pat. No. 5,689,384A, U.S. Pat. No. 6,542,325B, and U.S. Pat. No.7,876,521B can be used without any limitation.

A commercially available magnetic tape device generally includes amagnetic head and a servo head in accordance to a standard. In addition,a commercially available magnetic tape device generally has a servocontrolling mechanism for realizing head tracking of the timing-basedservo system in accordance to a standard. The magnetic tape deviceaccording to one aspect of the invention can be configured byincorporating the magnetic tape according to one aspect of the inventionto a commercially available magnetic tape device.

EXAMPLES

Hereinafter, the invention will be described with reference to Examples.However, the invention is not limited to aspects shown in Examples.“Parts” and “%” in the following description mean “parts by mass” and“mass %”, unless otherwise noted.

An average particle size of the invention and the specification is avalue measured by a method disclosed in paragraphs 0058 to 0061 ofJP2016-071926A. The measurement of the average particle size describedbelow was performed by using transmission electron microscope H-9000manufactured by Hitachi, Ltd. as the transmission electron microscope,and image analysis software KS-400 manufactured by Carl Zeiss as theimage analysis software.

Examples 1 to 9 and Comparative Examples 1 to 9

1. Preparation of Alumina Dispersion (Abrasive Liquid)

3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo ChemicalIndustry Co., Ltd.), 31.3 parts of 32% solution (solvent is a mixedsolvent of methyl ethyl ketone and toluene) of a polyester polyurethaneresin having a SO₃Na group as a polar group (UR-4800 manufactured byToyobo Co., Ltd. (amount of a polar group: 80 meq/kg)), and 570.0 partsof a mixed liquid of methyl ethyl ketone and cyclohexanone at 1:1 (massratio) as a solvent were mixed with 100.0 parts of alumina powder(HIT-80 manufactured by Sumitomo Chemical Co., Ltd., Mohs hardness of 9)having a gelatinization ratio of approximately 65% and a BET specificsurface area of 20 m²/g, and dispersed in the presence of zirconia beadsby a paint shaker for 5 hours. After the dispersion, the dispersionliquid and the beads were separated by a mesh and an alumina dispersion(abrasive liquid) was obtained.

2. Magnetic Layer Forming Composition List

Magnetic Solution

Ferromagnetic hexagonal ferrite powder (activation volume: see Table 4):100.0 parts

SO₃Na group-containing polyurethane resin: 14.0 parts

(Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g)

Dispersing agent: see Table 4

Cyclohexanone: 150.0 parts

Methyl ethyl ketone: 150.0 parts

Abrasive liquid

Alumina dispersion prepared in the section 1.: 6.0 parts

Silica Sol (Projection Formation Agent Liquid)

Colloidal silica (average particle size: 100 nm): 2.0 parts

Methyl ethyl ketone: 1.4 parts

Other Components

Stearic acid: 2.0 parts

Butyl stearate: 6.0 parts

Polyisocyanate (CORONATE (registered trademark) manufactured by NipponPolyurethane Industry): 2.5 parts

Finishing Additive Solvent

Cyclohexanone: 200.0 parts

Methyl ethyl ketone: 200.0 parts

The synthesis method or the like of the dispersing agent shown in Table4 will be described later in detail.

3. Non-Magnetic Layer Forming Composition List

Non-magnetic inorganic powder: α-iron oxide: 100.0 parts

Average particle size (average long axis length): 0.15 μm

Average acicular ratio: 7

BET specific surface area: 52 m²/g

Carbon black: 20.0 parts

Average particle size: 20 nm

SO₃Na group-containing polyurethane resin: 18.0 parts

(Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g)

Stearic acid: 1.0 part

Cyclohexanone: 300.0 parts

Methyl ethyl ketone: 300.0 parts

4. Back Coating Layer Forming Composition List

Non-magnetic inorganic powder: α-iron oxide: 80.0 parts

Average particle size (average long axis length): 0.15 μm

Average acicular ratio: 7

BET specific surface area: 52 m²/g

Carbon black: 20.0 parts

Average particle size: 20 nm

Vinyl chloride copolymer: 13.0 parts

Sulfonate group-containing polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Methyl ethyl ketone: 155.0 parts

Stearic acid: 3.0 parts

Butyl stearate: 3.0 parts

Polyisocyanate: 5.0 parts

Cyclohexanone: 355.0 parts

5. Preparation of Each Layer Forming Composition

(1) Preparation of Magnetic Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod.

A magnetic solution was prepared by performing beads dispersing of themagnetic solution components described above by using beads as thedispersion medium in a batch type vertical sand mill. Specifically, thedispersing process was performed for the dispersion retention time shownin Table 4 by using zirconia beads having a bead diameter shown in Table4, as the beads dispersion of each stage (first stage and second stage,or first to third stages). In the beads dispersion, dispersion liquidobtained by using filter (average hole diameter of 5 μm) was filteredafter completion of each stage. In the beads dispersion of each stage,the filling percentage of the dispersion medium was set to beapproximately 50 to 80 volume %.

The magnetic solution obtained as described above was mixed with theabrasive liquid, silica sol, other components, and the finishingadditive solvent and beads-dispersed for 5 minutes by using the sandmill, and ultrasonic dispersion was performed with a batch typeultrasonic device (20 kHz, 300 W) for 0.5 minutes. After that, theobtained mixed liquid was filtered by using a filter (average holediameter of 0.5 μm), and the magnetic layer forming composition wasprepared.

A circumferential speed of a tip of the sand mill at the time of beadsdispersion was in a range of 7 to 15 m/sec.

(2) Preparation of Non-Magnetic Layer Forming Composition

The non-magnetic layer forming composition was prepared by the followingmethod.

Each component excluding stearic acid, cyclohexanone, and methyl ethylketone was beads-dispersed by using a batch type vertical sand mill(dispersion medium: zirconia beads (bead diameter: 0.1 mm), dispersionretention time: 24 hours) to obtain dispersion liquid. After that, theremaining components were added into the obtained dispersion liquid andstirred with a dissolver. Then, the obtained dispersion liquid wasfiltered by using the filter (average hole diameter of 0.5 μm), and anon-magnetic layer forming composition was prepared.

(3) Preparation of Back Coating Layer Forming Composition

The back coating layer forming composition was prepared by the followingmethod.

Each component excluding stearic acid, polyisocyanate, and cyclohexanonewas kneaded and diluted by an open kneader. Then, the obtained mixedliquid was subjected to a dispersing process of 12 passes, with atransverse beads mill by using zirconia beads having a bead diameter of1 mm, by setting a bead filling percentage as 80 volume %, acircumferential speed of rotor tip as 10 m/sec, and a retention time for1 pass as 2 minutes. After that, the remaining components were addedinto the obtained dispersion liquid and stirred with a dissolver. Then,the obtained dispersion liquid was filtered with a filter (average holediameter of 1 μm) and a back coating layer forming composition wasprepared.

6. Manufacturing of Magnetic Tape and Formation of Timing-Based ServoPattern

The non-magnetic layer forming composition prepared in the section 5.(2) was applied to the surface of a support made of polyethylenenaphthalate having a thickness shown in Table 4 so that the thicknessafter the drying becomes the thickness shown in Table 4, to form anon-magnetic layer. Then, the magnetic layer forming compositionprepared in the section 5. (1) was applied onto the non-magnetic layerso that the thickness after the drying becomes the thickness shown inTable 4. In Examples and Comparative Examples in which “performed” wasshown in the column of the homeotropic alignment process in Table 4, thehomeotropic alignment process was performed by applying a magnetic fieldhaving a magnetic field strength of 0.3 T to the coating surface in avertical direction, while the coated magnetic layer forming compositionwas not dried, and then, the drying was performed to form the magneticlayer. In Comparative Examples in which “not performed” was shown in thecolumn of the homeotropic alignment process in Table 4, the coatedmagnetic layer forming composition was dried without performing thehomeotropic alignment process to form the magnetic layer.

After that, the back coating layer forming composition prepared in thesection 5. (3) was applied to the surface of the support made ofpolyethylene naphthalate on a side opposite to the surface where thenon-magnetic layer and the magnetic layer are formed, so that thethickness after the drying becomes the thickness shown in Table 4, anddrying was performed to obtain a laminate.

Then, a surface smoothing treatment (calender process) was performedwith respect to the obtained laminate with a calender roll configured ofonly a metal roll, at a calender process speed of 100 m/min, linearpressure of 294 kN/m (300 kg/cm), and a surface temperature of acalender roll shown in Table 4. As the calender process conditions arestrengthened (for example, as the surface temperature of the calenderroll increases), the magnetic layer surface Ra tends to decrease.

After that, a thermal treatment was performed in the environment of theatmosphere temperature of 70° C. for 36 hours. The laminate subjected tothe thermal treatment was cut to have a width of ½ inches (0.0127meters) by using a slitter, and a magnetic tape was obtained.

In a state where the magnetic layer of the manufactured magnetic tapewas demagnetized, servo patterns having disposition and shapes accordingto the LTO Ultrium format were formed on the magnetic layer by using aservo write head mounted on a servo testing machine. Accordingly, amagnetic tape including data bands, servo bands, and guide bands in thedisposition according to the LTO Ultrium format in the magnetic layer,and including servo patterns having the disposition and the shapeaccording to the LTO Ultrium format on the servo band was manufactured.

By doing so, each magnetic tape of examples and comparative examples wasobtained. The servo testing machine includes a servo write head and aservo head. This servo testing machine was also used in the evaluationwhich will be described later.

The thickness of each layer and the non-magnetic support and the totalthickness of the manufactured magnetic tape were acquired by thefollowing method. It was confirmed that the thickness of each layer isthe thickness shown in Table 4.

The cross section of the magnetic tape in a thickness direction wasexposed by an ion beam, and then, the cross section observation of theexposed cross section was performed with a scanning electron microscope.Various thicknesses were acquired as an arithmetical mean of thicknessesacquired at two positions in the thickness direction, in the crosssection observation.

7. Preparation of Dispersing Agent

Dispersing agents 1 to 4 shown in Table 4 were prepared by the followingmethod. Hereinafter, a temperature shown regarding the synthesisreaction is a temperature of a reaction liquid.

In Comparative Example 9, 2,3-dihydroxynaphthalene was used instead ofthe dispersing agents 1 to 4. 2,3-dihydroxynaphthalene is a compoundused as an additive for adjusting a squareness ratio in JP2012-203955A.

(1) Preparation of Dispersing Agent 1

Synthesis of Precursor 1

197.2 g of ε-caprolactone and 15.0 g of 2-ethyl-1-hexanol wereintroduced into a 500 mL three-neck flask and stirred and decomposedwhile blowing nitrogen. 0.1 g of monobutyltin oxide was added theretoand heated to 100° C. After 8 hours, the elimination of the raw materialwas confirmed by gas chromatography, the resultant material was cooledto room temperature, and 200 g of a solid precursor 1 (followingstructure) was obtained.

Synthesis of Dispersing Agent 1

40.0 g of the obtained precursor 1 was introduced into 200 mL three-neckflask, and stirred and decomposed at 80° C. while blowing nitrogen. 2.2g of meso-butane-1,2,3,4-tetracarboxylic dianhydride was added theretoand heated to 110° C. After 5 hours, the elimination of a peak derivedfrom the precursor 1 was confirmed by ¹H-NMR, and then, the resultantmaterial was cooled to room temperature, and 38 g of a solid reactionproduct 1 (mixture of the following structural isomer) was obtained. Thereaction product 1 obtained as described above is a mixture of thecompound 1 shown in Table 1 and the structural isomer. The reactionproduct 1 is called a “dispersing agent 1”.

(2) Preparation of Dispersing Agent 2

Synthesis of Dispersing Agent 2

The synthesis was performed in the same manner as in the synthesis ofthe dispersing agent 1, except for changing 2.2 g ofbutanetetracarboxylic acid anhydride and 2.4 g of pyromellitic aciddianhydride, and 38 g of a solid reaction product 2 (mixture of thefollowing structural isomer) was obtained. The reaction product 2obtained as described above is a mixture of the compound 2 shown inTable 1 and the structural isomer. The reaction product 2 is called a“dispersing agent 2”.

(3) Preparation of Dispersing Agent 3

Synthesis of Polyester (i-1)

12.6 g of n-octanoic acid (manufactured by Wako Pure ChemicalIndustries, Ltd.) as carboxylic acid, 100 g of ε-caprolactone (PLACCEL Mmanufactured by Daicel Corporation) as lactone, and 2.2 g of monobutyltin oxide (manufactured by Wako Pure Chemical Industries, Ltd.)(C₄H₉Sn(O)OH) were mixed with each other in a 500 mL three-neck flask,and heated at 160° C. for 1 hour. 100 g of ε-caprolactone was addeddropwise for 5 hours, and further stirred for 2 hours. After that, thecooling was performed to room temperature, and polyester (i-1) wasobtained.

The synthesis scheme will be described below.

Synthesis of Dispersing Agent 3 (Polyethyleneimine Derivative (J-1))

5.0 g of polyethyleneimine (SP-018 manufactured by Nippon Shokubai Co.,Ltd., number average molecular weight of 1,800) and 100 g of theobtained polyester (i-1) were mixed with each other and heated at 110°C. for 3 hours, to obtain a polyethyleneimine derivative (J-1). Thepolyethyleneimine derivative (J-1) is called a “dispersing agent 3”.

The synthesis scheme is shown below. In the following synthesis scheme,a, b, c respectively represent a polymerization molar ratio of therepeating unit and is 0 to 50, and a relationship of a+b+c=100 issatisfied. l, m, n1, and n2 respectively represent a polymerizationmolar ratio of the repeating unit, l is 10 to 90, m is 0 to 80, n1 andn2 are 0 to 70, and a relationship of l+m+n1+n2=100 is satisfied.

(4) Preparation of Dispersing Agent 4

Synthesis of Polyester (i-2)

Polyester (i-2) was obtained in the same manner as in the synthesis ofthe polyester (i-1), except for changing the amount of carboxylic acidshown in Table 3.

Synthesis of Dispersing Agent 4 (Polyethyleneimine Derivative (J-2))

A polyethyleneimine derivative (J-2) was obtained by performing thesynthesis which is the same as that of the compound J-1, except forusing polyethyleneimine shown in Table 2 and the obtained polyester(i-2). The polyethyleneimine derivative (J-2) is called a “dispersingagent 4”.

The weight-average molecular weight of the dispersing agents 1 and 2 wasmeasured by a method described above as the measurement method of theweight-average molecular weight of the compound represented by GeneralFormula 1. As a result of the measurement, the weight-average molecularweight of the dispersing agent 1 was 9,200 and the weight-averagemolecular weight of the dispersing agent 2 was 6,300.

The weight-average molecular weight of the dispersing agent 3(polyethyleneimine derivative (J-1)) and the dispersing agent 4(polyethyleneimine derivative (J-2)) was a value shown in Table 3, whenthe value was acquired by performing reference polystyrene conversion ofa value measured by GPC under the measurement conditions of the specificexample described above.

The weight-average molecular weight other than that described above is avalue acquired by performing reference polystyrene conversion of a valuemeasured by GPC under the following measurement conditions.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mm (internal diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

8. Measurement of Activation Volume

The powder in a powder lot which is the same as that of ferromagnetichexagonal barium ferrite powder used in the preparation of the magneticlayer forming composition was used as a measurement sample of theactivation volume. The magnetic field sweep rates of the He measurementpart at time points of 3 minutes and 30 minutes were measured by usingan oscillation sample type magnetic-flux meter (manufactured by ToeiIndustry Co., Ltd.), and the activation volume was calculated from therelational expression described above. The measurement was performed inthe environment of 23° C.±1° C. The calculated activation volume isshown in Table 4.

9. Measurement of Cos θ

A cross section observation sample was cut out from each magnetic tapeof Examples and Comparative Examples, and cos θ was acquired by themethod described above by using this sample. In each magnetic tape ofExamples and Comparative Examples, acquired cos θ is shown in Table 4.In each magnetic tape of Examples and Comparative Examples, a percentageof hexagonal ferrite particles having the aspect ratio and the length inthe long axis direction of the ranges described above which is ameasurement target of cos θ occupying all of the hexagonal ferriteparticles observed in the STEM image, was approximately 80% to 95% basedon the particle number.

The cross section observation sample used for the measurement of cos θwas manufactured by the following method.

(i) Manufacturing of Sample Including Protective Film

A sample including a protective film (laminated film of a carbon filmand a platinum film) was manufactured by the following method.

A sample having a size of a width direction 10 mm×longitudinal direction10 mm of the magnetic tape was cut out from the magnetic tape which is atarget acquiring the cos θ, with a blade. The width direction of thesample described below is a direction which was a width direction of themagnetic tape before the cutting out. The same applies to thelongitudinal direction.

A protective film was formed on the surface of the magnetic layer of thecut-out sample to obtain a sample including a protective film. Theformation of the protective film was performed by the following method.

A carbon film (thickness of 80 nm) was formed on the surface of themagnetic layer of the sample by vacuum deposition, and a platinum (Pt)film (thickness of 30 nm) was formed on the surface of the formed carbonfilm by sputtering. The vacuum deposition of the carbon film and thesputtering of the platinum film were respectively performed under thefollowing conditions.

Vacuum Deposition Conditions of Carbon Film

Deposition source: carbon (core of a mechanical pencil having a diameterof 0.5 mm)

Degree of vacuum in a chamber of a vacuum deposition device: equal to orsmaller than 2×10⁻³ Pa

Current value: 16 A

Sputtering Conditions of Platinum Film

Target: Pt

Degree of vacuum in a chamber of a sputtering device: equal to orsmaller than 7 Pa

Current value: 15 mA

(ii) Manufacturing Cross Section Observation Sample

A sample having a thin film shape was cut out from the sample includinga protective film manufactured in the section (i), by FIB processingusing a gallium ion (Ga⁺) beam. The cutting out was performed byperforming the following FIB processing two times. An accelerationvoltage of the FIB processing was 30 kV.

In a first FIB processing, one end portion (that is, portion includingone side surface of the sample including a protective film in the widthdirection) of the sample including a protective film in the longitudinaldirection, including the area from the surface of the protective film toa region of a depth of approximately 5 μm was cut. The cut-out sampleincludes the area from the protective film to a part of the non-magneticsupport.

Then, a microprobe was loaded on a cut-out surface side (that is, samplecross section side exposed by the cutting out) of the cut-out sample andthe second FIB processing was performed. In the second FIB processing,the surface side opposite to the cut-out surface side (that is, one sidesurface in the width direction) was irradiated with a gallium ion beamto perform the cutting out of the sample. The sample was fixed bybonding the cut-out surface of the second FIB processing to the endsurface of the mesh for STEM observation. After the fixation, themicroprobe was removed.

In addition, the surface of the sample fixed to the mesh, from which themicroprobe is removed, was irradiated with a gallium ion beam at thesame acceleration voltage described above, to perform the FIBprocessing, and the sample fixed to the mesh was further thinned.

The cross section observation sample fixed to the mesh manufactured asdescribed above was observed by a scanning transmission electronmicroscope, and the cos θ was acquired by the method described above.The cos θ acquired as described above is shown in Table 4.

10. Magnetic Layer Surface Ra

The measurement regarding a measurement area of 40 μm×40 μm wasperformed with an atomic force microscope (AFM, Nanoscope 4 manufacturedby Veeco Instruments, Inc.), and a center line average surface roughnessRa of the surface of the magnetic layer of the magnetic tape wasacquired. A scan speed (probe movement speed) was set as 40 μm/sec and aresolution was set as 512 pixel×512 pixel. The measurement results areshown in Table 4.

11. Evaluation of Squareness Ratio (SQ)

The squareness ratio of each magnetic tape manufactured was measured ata magnetic field strength of 1194 kA/m (15 kOe) by using an oscillationsample type magnetic-flux meter (manufactured by Toei Industry Co.,Ltd.). The measurement results are shown in Table 4.

12. Frequency of Occurrence of Signal Defects (Thermal Asperity) at theTime of Servo Signal Reproducing

The magnetic tape in which the timing-based servo pattern is formed wasattached to a servo testing machine. In the servo testing machine, themagnetic tape runs and the surface of the magnetic layer of the runningmagnetic tape is brought to come in to contact with and slide on theservo head mounted with the MR element, and accordingly, the servopatterns were read (servo signals were reproduced) by the servo head. Aportion of a reproduced waveform of the servo signal obtained by thereproduction which is not a normal burst signal and shows an outputequal to or greater than 200%, when an average value of the output at anoise level was set as 100%, was determined as the thermal asperity andthe number of times of the occurrence of the thermal asperity wascounted. A value (number of times/m) obtained by dividing the countednumber of times of the occurrence of the thermal asperity by the totallength of the magnetic tape was set as a thermal asperity occurrencefrequency. The measurement results are shown in Table 4.

The results described above are shown in Table 4.

TABLE 4 Ferromagnetic Magnetic solution beads hexagonal dispersionconditions ferrite First stage Second stage Third stage powderDispersion Dispersion Dispersion activation Dispersing agent retentionBead retention Bead retention Bead Homeotropic volume Content timediameter time diameter time diameter alignment [nm³] Type [part] [h][mm] [h] [mm] [h] [mm] process Comparative 2000 — — 10 0.5 — — — — NotExample 1 performed Comparative 2000 — — 10 0.5 — — — — Not Example 2performed Comparative 2000 — — 10 0.5 — — — — Not Example 3 performedComparative 2000 — — 10 0.5 — — — — Not Example 4 performed Comparative2000 — — 10 0.5 — — — — Not Example 5 performed Comparative 2000 — — 100.5 — — — — Not Example 6 performed Comparative 2000 — — 10 0.5 — — — —Not Example 7 performed Comparative 2000 — — 10 0.5 — — — — Not Example8 performed Comparative 2000 2,3- 12.0 10 0.5 10 0.1 Performed Example 9dihydroxynaphthalene Example 1 2000 Dispersion liquid 1 6.0 10 0.5 100.1 — — Performed Example 2 2000 Dispersion liquid 1 12.0 10 0.5 30 0.1— — Performed Example 3 2000 Dispersion liquid 1 12.0 10 0.5 10 0.1 100.05 Performed Example 4 2000 Dispersion liquid 2 6.0 10 0.5 10 0.1 — —Performed Example 5 2000 Dispersion liquid 3 6.0 10 0.5 10 0.1 — —Performed Example 6 2000 Dispersion liquid 4 6.0 10 0.5 10 0.1 — —Performed Example 7 2000 Dispersion liquid 1 6.0 10 0.5 10 0.1 — —Perforated Example 8 1600 Dispersion liquid 1 12.0 10 0.5 10 0.1 10 0.05Performed Example 9 1300 Dispersion liquid 1 12.0 10 0.5 10 0.1 10 0.05Performed Evaluation results Signal defects Surface (thermal temperatureBack Magnetic asperity) of Magnetic Non- Non- coating tape occurrencecalender layer magnetic magnetic layer Total frequency roll Thickness/layer support Thickness/ thickness/ Magnetic layer SQ Cos θ [number of °C. μm Thickness/μm Thickness/μm μm μm surface Ra/nm [—] [—] times/m]Comparative 100 0.10 1.00 4.30 0.60 6.00 1.8 0.58 0.68 0.07 Example 1Comparative 100 0.10 0.70 4.20 0.40 5.40 1.8 0.58 0.68 0.10 Example 2Comparative 90 0.10 0.70 4.20 0.30 5.30 2.2 0.58 0.68 0.05 Example 3Comparative 90 0.10 0.50 4.00 0.30 4.90 2.2 0.58 0.68 0.13 Example 4Comparative 100 0.10 0.70 4.20 0.30 5.30 1.8 0.58 0.68 1.10 Example 5Comparative 100 0.10 0.50 4.00 0.30 4.90 1.8 0.58 0.68 1.30 Example 6Comparative 105 0.10 0.70 4.20 0.30 5.30 1.6 0.58 0.68 4.50 Example 7Comparative 105 0.10 0.50 4.00 0.30 4.90 1.6 0.58 0.68 8.20 Example 8Comparative 105 0.10 0.50 4.00 0.30 4.90 1.6 0.78 0.80 1.20 Example 9Example 1 100 0.10 0.70 4.20 0.30 5.30 1.8 0.73 0.87 0.15 Example 2 1000.10 0.70 4.20 0.30 5.30 1.8 0.74 0.96 0.02 Example 3 100 0.10 0.70 4.200.30 5.30 1.8 0.74 0.98 0.01 Example 4 100 0.10 0.70 4.20 0.30 5.30 1.80.73 0.87 0.16 Example 5 100 0.10 0.70 4.20 0.30 5.30 1.8 0.73 0.85 0.18Example 6 100 0.10 0.70 4.20 0.30 5.30 1.8 0.73 0.85 0.18 Example 7 1050.10 0.50 4.00 0.30 4.90 1.6 0.73 0.87 0.16 Example 8 100 0.10 0.70 4.200.30 5.30 1.8 0.73 0.95 0.03 Example 9 100 0.10 0.70 4.20 0.30 5.30 1.80.73 0.95 0.02

With the comparison of Comparative Examples 1 to 4 and ComparativeExamples 5 to 9, it was confirmed that, in the case where the totalthickness of the magnetic tape is equal to or smaller than 5.30 μm andthe magnetic layer surface Ra is equal to or smaller than 1.8 nm, thefrequency of occurrence of signal defects decreases at the time of servosignal reproducing is significantly increased, compared to the casewhere the total thickness of the magnetic tape exceeds 5.30 μm(Comparative Examples 1 and 2) and the magnetic layer surface Ra exceeds1.8 nm (Comparative Examples 3 and 4).

With respect to this, in the magnetic tape of Examples 1 to 9, the totalthickness is equal to or smaller than 5.30 μm and the magnetic layersurface Ra is equal to or smaller than 1.8 nm, however, the frequency ofoccurrence of signal defects decreases at the time of servo signalreproducing was greatly decreased, compared to that of the magnetic tapeof Comparative Examples 5 to 9.

In addition, from the result shown in Table 4, an excellent correlationcan be confirmed between the cos θ and the frequency of occurrence ofsignal defects decreases at the time of servo signal reproducing, inwhich as the value of cos θ increases, the frequency of occurrence ofsignal defects decreases at the time of servo signal reproducingdecreases. In contrast, such a correlation was not observed between thesquareness ratio (SQ) and the frequency of occurrence of signal defectsdecreases at the time of servo signal reproducing as shown in Table 4.

An aspect of the invention can be effective in technical fields ofmagnetic tapes for high-density recording.

What is claimed is:
 1. A magnetic tape comprising: a non-magneticsupport; and a magnetic layer including ferromagnetic powder and abinder on the non-magnetic support, wherein the total thickness of themagnetic tape is equal to or smaller than 5.30 μm, the magnetic layerincludes a timing-based servo pattern, a center line average surfaceroughness Ra measured regarding a surface of the magnetic layer is equalto or smaller than 1.8 nm, the ferromagnetic powder is ferromagnetichexagonal ferrite powder, the magnetic layer includes an abrasive, and atilt cos θ of the ferromagnetic hexagonal ferrite powder with respect toa surface of the magnetic layer acquired by cross section observationperformed by using a scanning transmission electron microscope is 0.85to 1.00.
 2. The magnetic tape according to claim 1, wherein the cos θ is0.89 to 1.00.
 3. The magnetic tape according to claim 1, wherein themagnetic layer further includes a polyester chain-containing compoundhaving a weight-average molecular weight of 1,000 to 80,000.
 4. Themagnetic tape according to claim 1, wherein an activation volume of theferromagnetic hexagonal ferrite powder is 800 nm to 2,500 nm³.
 5. Themagnetic tape according to claim 1, wherein the center line averagesurface roughness Ra measured regarding a surface of the magnetic layeris 1.2 nm to 1.8 nm.
 6. The magnetic tape according to claim 1, whereinthe total thickness of the magnetic tape is 3.00 μm to 5.30 μm.
 7. Themagnetic tape according to claim 1, further comprising: a non-magneticlayer including non-magnetic powder and a binder between thenon-magnetic support and the magnetic layer.
 8. The magnetic tapeaccording to claim 1, further comprising: a back coating layer includingnon-magnetic powder and a binder on a side of the non-magnetic supportopposite to a side where the magnetic layer is provided.
 9. The magnetictape according to claim 1, wherein the abrasive includes alumina powder.10. A magnetic tape device comprising: a magnetic tape, a magnetic head;and a servo head, wherein the magnetic tape is a magnetic tapecomprising: a non-magnetic support; and a magnetic layer includingferromagnetic powder and a binder on the non-magnetic support, whereinthe total thickness of the magnetic tape is equal to or smaller than5.30 μm, the magnetic layer includes a timing-based servo pattern, acenter line average surface roughness Ra measured regarding a surface ofthe magnetic layer is equal to or smaller than 1.8 nm, the ferromagneticpowder is ferromagnetic hexagonal ferrite powder, the magnetic layerincludes an abrasive, and a tilt cos θ of the ferromagnetic hexagonalferrite powder with respect to a surface of the magnetic layer acquiredby cross section observation performed by using a scanning transmissionelectron microscope is 0.85 to 1.00.
 11. The magnetic tape deviceaccording to claim 10, wherein the cos θ is 0.89 to 1.00.
 12. Themagnetic tape device according to claim 10, wherein the magnetic layerfurther includes a polyester chain-containing compound having aweight-average molecular weight of 1,000 to 80,000.
 13. The magnetictape device according to claim 10, wherein an activation volume of theferromagnetic hexagonal ferrite powder is 800 nm³ to 2,500 nm³.
 14. Themagnetic tape device according to claim 10, wherein the center lineaverage surface roughness Ra measured regarding a surface of themagnetic layer is 1.2 nm to 1.8 nm.
 15. The magnetic tape deviceaccording to claim 10, wherein the total thickness of the magnetic tapeis 3.00 μm to 5.30 μm.
 16. The magnetic tape device according to claim10, wherein the magnetic tape further comprises a non-magnetic layerincluding non-magnetic powder and a binder between the non-magneticsupport and the magnetic layer.
 17. The magnetic tape device accordingto claim 10, wherein wherein the magnetic tape further comprises a backcoating layer including non-magnetic powder and a binder on a side ofthe non-magnetic support opposite to a side where the magnetic layer isprovided.
 18. The magnetic tape device according to claim 10, whereinthe abrasive includes alumina powder.